FILED
                                                           United States Court of Appeals
                                  PUBLISH                          Tenth Circuit

                    UNITED STATES COURT OF APPEALS                October 16, 2018

                                                              Elisabeth A. Shumaker
                          FOR THE TENTH CIRCUIT                   Clerk of Court
                      _________________________________

UNITED STATES OF AMERICA,

     Plaintiff - Appellee,

v.                                                  No. 17-3034

SHANE COX,

     Defendant - Appellant.

____________________

STATE OF KANSAS,

     Intervenor - Appellant.

–––––––––––––––––––––––––––––––––––

UNITED STATES OF AMERICA,

     Plaintiff - Appellee,

v.                                                  No. 17-3035

JEREMY KETTLER,

     Defendant - Appellant.

____________________

STATE OF KANSAS,

     Intervenor - Appellant.
                     _________________________________
                    Appeal from the United States District Court
                             for the District of Kansas
                         (D.C. No. 6:15-CR-10150-JTM)
                      _________________________________

Paige A. Nichols, Assistant Federal Public Defender (Melody Brannon, Federal Public
Defender, with her on the briefs), Topeka, Kansas, for Defendant–Appellant Shane Cox.

Joseph W. Miller of Law Offices of Joseph Miller, LLC, Fairbanks, Alaska (Robert J.
Olson, William J. Olson, Jeremiah L. Morgan, Herbert W. Titus of William J. Olson,
P.C., Vienna, Virginia, with him on the briefs) for Defendant–Appellant Jeremy Kettler.

Derek Schmidt, Attorney General of Kansas, Jeffrey A. Chanay, Chief Deputy Attorney
General, Toby Crouse, Solicitor General of Kansas, Dwight R. Carswell and Bryan C.
Clark, Assistant Solicitors General, Topeka, Kansas, for Intervenor–Appellant.

Elizabeth H. Danello, Attorney, Appellate Section, Criminal Division, Department of
Justice, Washington, D.C. (Stephen R. McAllister, United States Attorney, District of
Kansas, Jared S. Maag, Assistant United States Attorney, District of Kansas, Kenneth A.
Blanco, Acting Assistant Attorney General, and Trevor N. McFadden, Deputy Assistant
Attorney General, Department of Justice, Washington, D.C., with her on the brief) for
Plaintiff–Appellee.
                       _________________________________

Before HARTZ, SEYMOUR, and PHILLIPS, Circuit Judges.
                  _________________________________

PHILLIPS, Circuit Judge.
                     _________________________________

      This is a tale of two laws: the National Firearms Act (NFA), 26 U.S.C.

§§ 5801–5872, which requires the registration of statutorily defined firearms, and

Kansas’s Second Amendment Protection Act (SAPA), ch. 100, 2013 Kan. Sess. Laws

vol. 1 500–03 (codified at Kan. Stat. Ann. §§ 50-1201 to -1211 (2014)), which

purports to exempt any personal firearm, firearm accessory, or ammunition

manufactured, owned, and remaining within Kansas’s borders from “any federal

law, . . . including any federal firearm or ammunition registration program, under the

                                           2
authority of congress to regulate interstate commerce.” Kan. Stat. Ann. § 50-1204(a).

In 2014, these two laws intersected when the government prosecuted two Kansas

men, Shane Cox and Jeremy Kettler, for violating the NFA by manufacturing (in

Kansas), transferring (in Kansas), and possessing (in Kansas) several unregistered

firearms. A jury found them guilty of most (though not all) of the charges.

      Now, Cox and Kettler appeal their convictions, though they don’t dispute that

their actions ran afoul of the NFA.1 First, they challenge the NFA’s constitutionality,

alleging that the statute is an invalid exercise of congressional power and an invasion

of the Second Amendment right to bear arms. Second, they challenge the district

court’s ruling that their reliance on the SAPA, which they understood to shield

Kansas-made and -owned firearms from federal regulation, provided no defense to

charges that they violated the NFA. Kettler further asks us to see his prosecution as

the product of a dispute between Kansas and the federal government over the SAPA,

a dispute that unjustly swept him up (along with Cox, though Cox hasn’t joined this

argument). We also granted Kansas’s request to participate in these appeals as needed

to defend the SAPA from a Supremacy Clause challenge.




      1
        Cox and Kettler each appealed individually (in cases nos. 17-3034 and
17-3035, respectively), but because their appeals raise overlapping issues, we granted
the government leave to file a single response brief. We consider Cox’s and Kettler’s
appeals companioned cases (though we never formally consolidated them), separately
submitted to the same panel for oral argument and decision.

                                           3
      We reject Cox’s and Kettler’s challenges to their convictions (without

addressing the SAPA’s constitutionality). Exercising jurisdiction under 28 U.S.C.

§ 1291, we therefore affirm the district court’s judgments.

                                   BACKGROUND

      In 2014, Shane Cox ran Tough Guys, an army-surplus store in Chanute,

Kansas. Inside the store, near a glass display case filled with homemade silencers,

Cox had posted a copy of the SAPA (which the Kansas legislature passed a year

earlier) for his customers to read. See Kan. Stat. Ann. §§ 50-1201 to -1211. Drawing

on the Second, Ninth, and Tenth Amendments to the U.S. Constitution, as well as the

Kansas Constitution’s bill of rights, the SAPA purports to protect from federal

interference the availability of all firearms, firearm accessories (including silencers2),

and ammunition made, sold, and kept “within the borders of Kansas.” Kan. Stat. Ann.

§§ 50-1202, 50-1203(b), 50-1204(a), 50-1206 to -1208; see also Kan. Const. Bill of

Rights § 4 (guaranteeing an individual right to bear arms).

      The display caught the attention of Jeremy Kettler, an army veteran from

neighboring Humboldt who’d walked into Tough Guys to look around. Cox was in


      2
         The Kansas law uses the term “sound suppressors” instead of “silencers.”
See, e.g., Kan. Stat. Ann. § 50-1203(b). Kettler, too, prefers “suppressor” to “the
more colloquial term ‘silencer,’” explaining that “while such a device will ‘suppress’
the noise of a gunshot to below a level that would cause hearing damage,” it
“come[s] nowhere close to ‘silencing’ the sound of a gunshot, as is depicted in
television and movies.” Kettler’s Opening Br. at 10 n.5. But the NFA uses “silencer,”
as does Cox. 26 U.S.C. § 5845(a)(7); see also, e.g., Cox’s Opening Br. at 2. So for
consistency’s sake (and without expressing an opinion on either term’s accuracy), we
adopt “silencer” throughout this opinion.

                                            4
the store, so Kettler asked him about the law and the silencers. Neither Cox nor

Tough Guys held a federal firearms license, but Cox believed that as a result of the

SAPA, he could avoid the “red tape” of federal firearms regulations as long as the

silencers never left Kansas. Cox R. vol. 3 at 292:9–11. Kettler bought one of Cox’s

silencers and later praised it (and Tough Guys) in a Facebook post.

      In December 2014, the Bureau of Alcohol, Tobacco, Firearms and Explosives

(ATF) learned that Tough Guys was selling unregistered silencers and started an

investigation. Within a year, federal prosecutors secured a grand jury indictment

against Cox and Kettler, charging them with thirteen crimes linked to Cox’s firearms-

manufacturing venture, Kettler’s patronage of it, and the ensuing investigation. Count

1 alleged that Kettler had knowingly and willfully made false statements “[d]uring a

[f]ederal [i]nvestigation,” in violation of 18 U.S.C. § 1001. Cox R. vol. 1 at 28.

Counts 2, 3, and 4 each charged Cox with possessing an unregistered firearm—a

destructive device, a short-barreled rifle, and another destructive device,3

respectively—in violation of 26 U.S.C. § 5861(d). Count 5 accused both Cox and

Kettler of conspiring, under 18 U.S.C. § 371, to violate the NFA by building and

selling an unregistered silencer. Counts 6, 7, 8, 9, and 11 charged Cox with five

violations of 26 U.S.C. § 5861(e) for transferring five silencers—four to recipients


      3
        The NFA defines a destructive device as “any explosive, incendiary, or
poison” gas, bomb, grenade, rocket, mine, or similar device, as well as “any
combination of parts either designed or intended” to be converted into such a device.
26 U.S.C. § 5845(f). Prosecutors alleged that Cox had kept some “grenade husks,”
accelerant, and other components in his workshop. Cox R. vol. 3 at 221:14.

                                           5
identified by their initials plus a fifth to “an undercover law enforcement officer.”

Cox R. vol. 1 at 34. Count 10 accused Cox of making a silencer in violation of 26

U.S.C. § 5861(f). Count 12 alleged that between June 20, 2014, and February 4,

2015, Cox had “engaged in the business of manufacturing and dealing in” silencers in

violation of 26 U.S.C. § 5861(a). Cox R. vol. 1 at 34. And count 13 charged Kettler

with possessing a silencer in violation of 26 U.S.C. § 5861(d).

      Cox and Kettler each pleaded not guilty and moved to dismiss the NFA-based

charges,4 claiming—for slightly different reasons—that the SAPA shielded them

from criminal liability for running afoul of federal firearms regulations.5 Cox argued

that because of the SAPA, enforcing the NFA against him would exceed the federal

government’s constitutional authority and usurp “powers reserved to the States” in

violation of the Tenth Amendment. Cox R. vol. 1 at 39. Kettler, in turn, asserted

entrapment by estoppel. By enacting the SAPA, argued Kettler, the Kansas

legislature had “specifically” told him that federal laws didn’t apply to his Kansas-

made and -owned suppressor, and his reasonable reliance on Kansas’s promise

rendered the federal prosecution unjust. 

      The district court rejected both arguments in one written order. See United

States v. Cox (Cox I), 

, 1285–88 (D. Kan. 2016). First it ruled,


      4
          Kettler didn’t contest count 1, the false-statement charge.
      5
         Cox and Kettler also each moved “to join in any and all motions and
memoranda” filed by the other. Cox R. vol. 1 at 62; Kettler R. vol. 1 at 65. The
district court granted their motions.

                                             6
based on Supreme Court and circuit precedent, that the NFA was a valid exercise of

Congress’s taxing power. 

Next the court threw out Kettler’s

entrapment-by-estoppel defense, reasoning that because state officials lack the power

to construe or enforce federal law, it wasn’t reasonable for Kettler to rely on the

Kansas legislature’s representations about the reach of federal law. 

The court therefore denied the motions to dismiss the indictment. 

      A few months later, the government submitted a pre-trial motion asking the

court to “find that any defense based on Kansas’ enactment of the [SAPA] is not a

valid legal defense.” Cox R. vol. 1 at 106. And to keep the Kansas statute from

confusing matters for the jury, the government sought “a prohibition on any mention”

of the SAPA. 

at 16:21–22. The court initially granted the government’s

request, but then tempered that ruling in response to Kettler’s offer of proof, which

convinced the court that “references to [the] SAPA [we]re interwoven with the

evidence of the alleged offenses.”6 

at 194. The court maintained that the

SAPA “provide[d] no defense” to the charged offenses, 

but it declined to

“excise” the SAPA from the evidence and predicted that some mention of the law

would be admissible to contextualize the charged offenses, 

And if (as the



      6
        Kettler’s proffer of SAPA-related evidence included: (1) that Cox handed out
copies of the SAPA to customers, including Kettler, who bought silencers; (2) that
Kettler knew about the SAPA and relied on it; (3) that an ATF agent who’d talked to
Kettler on the phone learned that Kettler “was confused as to the investigation into
Cox and his silencers because of the existence of the State law”; and (4) that Cox had
informed Kettler of the SAPA when the two discussed silencers. Cox R. vol. 1 at 133.

                                           7
court assumed) the SAPA surfaced at trial, the court promised to instruct jurors on

how to consider the law.

       The state of Kansas, meanwhile, moved to intervene. Federal law gives a state

the right to intervene “[i]n any action, suit, or proceeding in a court of the United

States . . . wherein the constitutionality of any statute of that State affecting the

public interest is drawn in question.” 28 U.S.C. § 2403(b). So far in this case, the

district court had neither ruled nor been asked to rule on the SAPA’s

constitutionality. Yet considering the breadth of the words “drawn into question,” the

court decided to grant Kansas’s motion to intervene. Cox R. vol. 1 at 197 (quoting 28

U.S.C. § 2403(b)). Kansas couldn’t present evidence or directly participate in the

trial, but the court’s order allowed the state “to be heard on any subsequent rulings

that implicate[d] the constitutionality of [the] SAPA.” 

proceeded to a joint trial in November 2016. After Cox rested on the

third day, and again after Kettler rested on the fourth, both moved for judgments of

acquittal. The court ultimately dismissed the conspiracy charge against both

defendants, having seen “no evidence . . . of a conspiracy between Mr. Cox and

Mr. Kettler,” and the false-statement charge against Kettler. Cox R. vol. 3 at 565. Yet

it found that the government had presented sufficient evidence to send the remaining

counts to the jury.

       The jury began deliberating on the fourth day, and it returned a verdict later

the same day, finding Cox not guilty of the destructive-device-possession counts (2

and 4) but guilty of the remaining eight counts: unlawfully possessing a short-

                                             8
barreled rifle in count 3; unlawfully transferring silencers in counts 6, 7, 8, 9, and 11;

unlawfully making a silencer in count 10; and unlawfully engaging in business as a

dealer or manufacturer of silencers in count 12. The jury also found Kettler guilty of

the remaining count against him, unlawfully possessing a silencer in count 13.

      The day before the court submitted the case to the jury, Kettler (joined by Cox)

filed a motion “to dismiss the present prosecution.” Cox R. vol. 1 at 218. They

argued that because the NFA provisions at issue—26 U.S.C. §§ 5861 and 5871,

which lay out prohibitions and penalties—had “become merely regulatory

punishment,” the provisions exceeded Congress’s power to tax and, in fact, usurped

power that the Tenth Amendment reserved to the states. 

The motion

doesn’t mention the Second Amendment, but after Kansas submitted a response

defending the SAPA on Second Amendment grounds, Kettler filed a reply relying

almost exclusively on that amendment and urging the court to find that the NFA

unconstitutionally infringed the right to bear arms.

      The district court addressed both arguments in a January 2017 written order.

United States v. Cox (Cox II), 

, 1222–23 (D. Kan. 2017). The

court reiterated its conclusion, based on Supreme Court precedent, that the NFA is a

valid exercise of Congress’s taxing power. 

accord Cox 

, 1287. And “if the NFA is otherwise consistent with the Constitution and

constitutes a valid exercise of Congress’s taxing power,” the court reasoned, “then it

does not run afoul of the Tenth Amendment.” Cox 

. Next,

the court concluded that none of the NFA provisions that applied to Cox and Kettler

                                            9
infringed their Second Amendment rights. 

The court therefore denied

the motion to dismiss. 

      The following month, the district court held a sentencing hearing. At that

hearing, the court took into account Cox’s and Kettler’s reliance on the SAPA and

gave them the benefit of that reliance. In lieu of prison time, the court sentenced Cox

to two years’ probation and Kettler to one year’s.

      Cox and Kettler appealed their convictions, and Kansas “move[d] to

participate as a party” in Cox’s appeal, citing 28 U.S.C. § 2403(b) and

Fed. R. App. P. 44(b). State of Kan.’s Mot. to Participate as Party at 1–2, United

States v. Cox, No. 17-3034 (10th Cir. May 9, 2017). The SAPA “ha[d] played a

prominent role in [Cox’s] case,” Kansas noted, and the federal government had

“argued at every turn that the [SAPA] is ‘clearly preempted by federal law’ and

‘invalid.’” 

(quoting Cox R. vol. 1 at 87, 108). Kansas therefore asked to

submit briefs, on the same schedule as Cox, defending the SAPA’s constitutionality.

No one opposed the motion, so we granted it, and Kansas filed two briefs.

                                      DISCUSSION

      Though Cox and Kettler challenge their convictions, neither denies that he

failed to abide by the NFA’s rules: Kettler possessed an unregistered silencer; Cox

possessed an unregistered short-barreled rifle and dealt in unregistered silencers.

They strike instead at the NFA itself, arguing that the Act exceeds the constitutional

bounds of Congress’s power and violates their Second Amendment rights. In the

alternative, even if the NFA passes constitutional muster, they contend that their

                                          10
reliance on the SAPA mitigates their culpability for violating the NFA—a defense

that, they claim, the district court erroneously kept from the jury.7 We address the

NFA’s constitutionality first; then we turn to the SAPA and how (if at all) it affected

Cox’s and Kettler’s culpability.

A. The Constitutionality of the National Firearms Act

      Cox and Kettler claim that the NFA—at least as applied to their conduct8—

suffers two constitutional infirmities, both fatal. We review each challenge de novo.




      7
          Kansas, in turn, briefed these issues:

      1. Does the National Firearms Act, specifically 26 U.S.C. § 5861,
         preempt the Second Amendment Protection Act?
      2. Did the District Court err in holding that the Second Amendment does
         not protect possession of silencers?

Br. of Intervenor State of Kan. at 1 (Br. of Kan.). As for the first issue, though,
preemption isn’t relevant here, and we needn’t address the SAPA’s constitutionality.
And as for the second issue, it’s not clear how the Second Amendment’s protection
of silencers would advance the SAPA’s constitutionality. As a result, we don’t
directly engage any of Kansas’s arguments.
      8
         Kettler isn’t clear about whether he’s mounting a facial or an as-applied
challenge to the NFA, while Cox specifically claims that the NFA “as applied”
exceeds Congress’s powers and violates the Second Amendment. Cox’s Opening Br.
at 36, 52. It’s harder to prevail on a facial challenge—unlike an as-applied challenge,
a facial challenge fails if “at least some” constitutional applications of the challenged
statute exist. Wash. State Grange v. Wash. State Republican Party, 

, 457
(2008) (quoting Schall v. Martin, 

, 264 (1984)). And Kettler focuses on
the NFA’s transfer provisions, such as 26 U.S.C. § 5811, rather than take on the
statute as a whole. So, in the absence of an indication that we should do otherwise,
we treat both Cox’s and Kettler’s constitutional challenges as challenges to the NFA
as it applied to them. (We also note that the failure of an as-applied challenge shows
that the statute has “at least some” constitutional applications, spelling the end of any
facial challenge.)

                                             11
United States v. Reese, 

, 799 (10th Cir. 2010) (quoting United States v.

Dorris, 

, 584 (10th Cir. 2000)).

       1. Is the National Firearms Act a Valid Exercise of Congressional Power?

       Cox and Kettler argue that the NFA exceeds Congress’s power. We agree with

the government, though: the NFA is a valid exercise of Congress’s taxing power, as

well as its authority to enact any laws “necessary and proper” to carry out that power.

U.S. Const. art. I, § 8, cls. 1, 18.

       Among other enumerated powers, Article I of the Constitution gives Congress

the “Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts

and provide for the common Defence and general Welfare of the United States,” 

and “To make all Laws which shall be necessary and proper for carrying into

Execution the foregoing Power[],” 

       And on its face, the NFA is a taxing scheme. The statute collects occupational

and excise taxes from businesses and transactions involving listed firearms—which

include short-barreled rifles, silencers, and destructive devices. See 26 U.S.C.

§ 5845(a) (defining “firearm”). Importers, manufacturers, and dealers of these

firearms must pay a yearly tax of $500 to $1,000. 

And each time one of

these firearms is made or transferred, the statute levies a $200 tax. 

(“Transfer tax”); 

(“Making tax”). But the NFA does more than lay taxes.

To carry out the taxing scheme, it also mandates the registration of every importer,

manufacturer, and dealer, see 

and of every firearm made, see 

or transferred, see 

And to ensure compliance, the statute has teeth: the

                                           12
failure to abide by any of its rules is a crime punishable by up to ten years in prison

(or a fine, or both). 

(“Prohibited acts”), 5871 (“Penalties”).

       The Supreme Court addressed Congress’s taxing-clause authority to enact the

NFA eighty-one years ago, when a firearms dealer indicted for failing to pay the

(then $200) annual dealer tax challenged the statute’s constitutional basis with an

argument similar to Cox and Kettler’s. See United States v. Sonzinsky, 

,

511 (1937). The dealer conceded that the taxing power allowed Congress to tax

firearms dealers, yet he “insist[ed]” that the tax at issue was “not a true tax, but a

penalty imposed for the purpose of suppressing traffic in a certain noxious type of

firearms.” 

But the Constitution, according to the dealer, had reserved

regulation of these firearms to the states, not to the federal government. 

that the NFA revealed its “penal and prohibitive character” by

cumulatively taxing importers, manufacturers, dealers, and transferors. 

Court rejected the dealer’s challenge, refusing to conclude that

the NFA—on its face a taxing measure—exceeded congressional power “by virtue of

its deterrent effect on the activities taxed.” 

“Every tax is in some

measure regulatory,” explained the Court, and “a tax is not any the less a tax because

it has a regulatory effect.” 

Unlike the child-labor tax struck down in the

Child Labor Tax Case, the NFA tax wasn’t “a penalty resorted to as a means of

enforcing [other] regulations.” 

v. Drexel Furniture Co. (The Child

Labor Tax Case), 

, 35 (1922)). Rather, though the NFA contained

registration provisions, those provisions were “obviously supportable as in aid of a

                                            13
revenue purpose.” 

the $200-per-year dealer tax produced “some

revenue,” the Court refused to ponder Congress’s motives in imposing it or to

estimate its regulatory effect. 

In sum, since “it [wa]s not attended by an

offensive regulation, and since it operate[d] as a tax,” the Court concluded that the

NFA’s taxing scheme was “within the national taxing power.” 

Kettler urge us to limit Sonzinsky’s holding to the NFA of 1937, a

statute that they claim no longer exists, and to reconsider the constitutional premise

for today’s NFA. According to Cox and Kettler, the statute that Sonzinsky upheld

“has morphed, over more than eight decades, to the point that the current NFA

registration system bears virtually no resemblance to a measure designed to collect

revenue.” Kettler’s Opening Br. at 11–12.

      Today, Cox and Kettler contend, the NFA is “far more of a gun-control

measure than a gun-tax measure.” Cox’s Opening Br. at 53. They point out that since

2003, the ATF has administered the NFA from the Justice Department instead of the

Treasury Department, where the ATF and its predecessor agencies spent the

preceding 200 years. They note that as a result, the NFA—alone in the Internal

Revenue Code—now falls outside the purview of the Treasury Secretary. And with

this shift in oversight, they argue, today’s NFA resembles the regulatory scheme

struck down in the Child Labor Tax Case, which subjected employers “to inspection

at any time not only by the taxing officers of the Treasury, the Department normally

charged with the collection of taxes, but also by the Secretary of Labor and his

subordinates, whose normal function is the advancement and protection of the

                                           14
welfare of the 

. Cox and Kettler thus conclude that the NFA,

like that “so-called tax” on child labor, is really a penalty, outside Congress’s taxing

power. The Child Labor Tax 

.

      Which agency or agencies administer a tax, however, is but one indicator

among several in the “functional approach” to whether that tax is really—for

constitutional purposes—a tax. See Nat’l Fed. of Indep. Bus. v. Sebelius, 

, 565 (2012). And on that score, the child-labor “tax” in the Child Labor Tax

Case had two more strikes against it: first, the tax imposed “a heavy exaction” on

violators, equal to one tenth of a business’s yearly net income; and second, the law

included a scienter requirement, meaning that only knowing violators had to pay the

tax. The Child Labor Tax 

; see also 

–

66. The sum of all three characteristics made “palpable” the law’s “prohibitory and

regulatory effect” and convinced the Court that the so-called tax was really a penalty,

meant to stop child labor, and fell outside Congress’s taxing-clause authority. The

Child Labor Tax 

, 39.

      Yet Cox and Kettler don’t contend that today’s NFA exhibits either of the

other penalty-like features of the child-labor “tax” in the Child Labor Tax Case. Nor

need we assess which way those features point in this case, for we aren’t starting

from a blank slate in determining whether the NFA is a constitutional tax; we’re

starting from Sonzinsky. In upholding the NFA, Sonzinsky expressly distinguished the

Child Labor Tax Case and similar decisions, in which “the [challenged] statute

contain[ed] regulatory provisions related to a purported tax in such a way . . . that the

                                           15
latter [wa]s a penalty resorted to as a means of enforcing the regulations.” 

. The NFA, according to Sonzinsky, regulates only “in aid of a

revenue purpose.” 

years ago, Sebelius reaffirmed the NFA’s constitutional legitimacy,

touting the statute’s “obviously regulatory” tax on sawed-off shotguns as proof that

“taxes that seek to influence conduct are nothing new” and remain valid exercises of

the taxing 

(citing 

); see also 

even though the Affordable Care Act’s individual mandate “seeks to

shape decisions about whether to buy health insurance,” it’s still a valid exercise of

the taxing power). And by itself, moving the NFA’s administration from the Treasury

Department to the Justice Department didn’t so alter the balance between the

statute’s taxes and its regulatory provisions as to unmoor today’s NFA from the

statute deemed constitutional in Sonzinsky and cited with approval in Sebelius.

      But Cox and Kettler’s taxing-power argument has another angle. Noting that

Sonzinsky upheld the NFA’s dealer tax in large part because the tax produced “some

revenue,” they dispute that the administration of today’s NFA raises any net revenue.

. Citing our decision in United States v. Dalton, 

(10th Cir. 1992), they claim that a statute that doesn’t raise net revenue can’t “be

justified under Congress’ power to raise revenue.” Kettler’s Opening Br. at 24.

      The current registration process, they argue, is “structured to avoid generating

revenue in as many instances as possible.” 

They claim that increasingly

complex registration applications, background checks, and swelling (now months-

                                           16
long) delays likely discourage many from even trying to register and pay NFA taxes.

As for those willing to run that gantlet, Cox and Kettler note that the ATF denies the

applications of would-be registrants whom federal law prohibits from buying

firearms, meaning that “literally tens of millions of Americans are deemed ineligible

to pay the NFA tax.” Kettler’s Opening Br. at 18 (citing 18 U.S.C. § 922(d), which

makes it unlawful “for any person to sell or otherwise dispose of any firearm” to

someone who falls into any of nine categories, including felons, see 

and fugitives from justice, see 

And what’s more, Congress hasn’t

raised the $200 transfer fee for silencers and short-barreled rifles since 1934—not

even to keep pace with inflation9—so, argue Cox and Kettler, “it could be said that”

the NFA’s taxes are now “productive of no net revenue.” 

2.

      But Dalton doesn’t stand for the proposition that Cox and Kettler attribute to

it: that “the taxing power can no longer be the constitutional basis for the NFA when

the $510 and $200 NFA fees no longer raise net revenue.” Kettler’s Opening Br. at 24.




      9
        Cox and Kettler recognize that Congress has raised the occupational taxes
that importers, manufacturers, and dealers must pay.
      10
          The NFA imposes a transfer tax of $5 “on any firearm classified as any other
weapon under [26 U.S.C.] section 5845(e).” 26 U.S.C. § 5811(a). But the weapons
listed in Cox’s and Kettler’s indictment—silencers, a short-barreled rifle, destructive
devices—don’t fall under § 5845(e)’s definition of “any other weapon.” 26 U.S.C.
§ 5845. They are “firearms” taxed at $200 per transfer, see § 5811(a), so the $5 rate
is irrelevant to Cox’s and Kettler’s as-applied challenges to the NFA.

                                          17
      That case addressed whether due process permitted Dalton’s convictions for

violating the NFA by possessing (26 U.S.C. § 5861(d)) and transferring (§ 5861(e))

an unregistered machinegun, when a separate law, 18 U.S.C. § 922(o), banned the

possession and transfer of machineguns. 

. To avoid running

afoul of 26 U.S.C. § 5861(d) and (e), the NFA’s transfer provision (§ 5812) required

the transferor to pay a tax and apply to register the machinegun. 

. But the transfer provision also required that applications to register illegal

weapons be denied. 

Section 922(o) thus made compliance with § 5861(d)

and (e)’s registration requirements impossible, and we agreed with Dalton “that it

violate[d] fundamental fairness to convict him for failing to do an act which everyone

agree[d] he could not perform.” 

. Weakening the premise for

Dalton’s convictions still further, we reasoned that § 922(o) had “undercut the

constitutional basis” of the NFA’s machinegun-registration requirement. 

25 (quoting United States v. Rock Island Armory, Inc., 

, 125 (C.D.

Ill. 1991), rejected by United States v. Ross, 

, 1194 (7th Cir. 1993),

vacated, 

(1994)).11 We noted that Sonzinsky had upheld the NFA’s

registration requirements as “solely in aid of collecting the tax,” so when § 922(o)


      11
          The Supreme Court returned Ross to the Seventh Circuit for reconsideration
in light of the Court’s intervening decision in Staples v. United States, 

,
602 (1994), which interpreted 26 U.S.C. § 5861(d) to require a defendant to know
that the weapon that he possessed exhibited features making it a “firearm” for NFA
purposes. Ross v. United States, 

(1994); see also United States v.
Ross, 

, 145 (7th Cir. 1994) (concluding, on remand, that failing to
instruct the jury on this knowledge requirement warranted a new trial).

                                           18
ended the registration and taxation of machineguns, it also removed “the

constitutional base for those requirements—i.e., the power to tax.” 

Dalton’s convictions for possessing and transferring an unregistered machinegun in

violation of § 5861(d) and (e), we concluded, were therefore “constitutionally

infirm.” 

       As later decisions have made clear, the constitutional infirmity in Dalton’s

convictions resulted from 18 U.S.C. § 922(o)’s prohibition of the firearm at issue,

which removed 26 U.S.C. § 5861’s constitutional footing by making registration “a

literal and legal impossibility.” United States v. McCollom, 

, 971 (10th

Cir. 1993). Unless a separate statute criminalizes possession of a firearm, though, a

due-process or taxing-power challenge to a § 5861(d) conviction is doomed to fail.

See 

(concluding that, because no statute bans the registration of short-

barreled shotguns, due process didn’t bar McCollum’s § 5861(d) conviction for

possessing an unregistered sawed-off shotgun). That’s so regardless of the practical

difficulty or unlikelihood of registering the firearm—and regardless of how little

revenue the tax generates. See, e.g., United States v. Berres, 

, 1088

(10th Cir. 2015) (reasoning that the registration of flash bangs isn’t a legal

impossibility, and so rejecting a due-process challenge to Berres’s § 5861(d)

conviction for possessing one); United States v. Eaton, 

, 1236 (10th

Cir. 2001) (reaching the same conclusion regarding Eaton’s possession of a pipe

bomb). And because Cox and Kettler point to no federal statutory ban on the



                                           19
possession or transfer of the firearms at issue—silencers and short-barreled rifles—

Dalton doesn’t control this case.

      Nevertheless, Cox and Kettler urge us to extend Dalton to this case by treating

a lack of net revenue from NFA taxes on a weapon like a statutory ban on that

weapon. As net revenue falls to zero, they argue, the NFA’s taxing purpose

disappears, leaving only its regulatory effect, and the statute’s constitutional

legitimacy crumbles.

      They’re correct that revenue mattered in Dalton, which reasoned that because

of § 922(o)’s machinegun ban, the government collected none from the possession or

transfer of 

. Revenue also mattered in 

, which upheld the NFA because its dealer tax was “productive of some

revenue,” and in 

, which noted that the ACA’s shared-

responsibility payment bore “the essential feature of any tax: It produce[d] at least

some revenue for the Government.”

      But in each case, the constitutional question hinged on gross revenue, and it

set the bar low—“some” gross revenue. See Minor v. United States, 

, 98

n.13 (1969) (“A statute does not cease to be a valid tax measure . . . because the

revenue obtained is negligible . . . .”). Cox and Kettler direct us to no authority where

a tax’s net revenue (i.e., what’s left after deducting expenses) affects its

constitutional validity. Plus, as the government pragmatically puts it, “If the focus

were on net revenue, then the Executive Branch could negate the constitutionality of

a tax imposed by Congress simply through spendthrift enforcement.” Br. for the

                                            20
United States at 21. While Cox and Kettler contend that the $200 transfer tax on

silencers “no longer raise[s] net revenue,” they do not dispute that it raises some

revenue. Kettler’s Opening Br. at 24. That’s all that Sonzinsky and Sebelius require

(and what we deemed impossible in Dalton).

      Accordingly, though times may have changed since the Court decided

Sonzinsky in 1937, Cox and Kettler point to no differences, either in the NFA or in

courts’ understanding of the national taxing power, that justify departing from

Sonzinsky’s conclusion that the NFA is a valid exercise of Congress’s power. See

Citizens United v. FEC, 

, 278 (D.D.C. 2008) (“Only the Supreme

Court may overrule its decisions.”); see also Rodriguez de Quijas v. Shearson/Am.

Express, Inc., 

, 484 (1989) (explaining that courts of appeals should

follow Supreme Court precedent that “has direct application in a case” even if that

precedent “appears to rest on reasons rejected in some other line of decisions” and

should “leav[e] to th[e] Court the prerogative of overruling its own decisions”). We

therefore conclude that the NFA falls within Congress’s power to tax.12




      12
         Other circuits uniformly agree. See, e.g., United States v. Spoerke, 

, 1245–46 (11th Cir. 2009); United States v. Vill. Ctr., 

, 950 (8th
Cir. 2006); United States v. Lim, 

, 913–14 (7th Cir. 2006); United States
v. Thompson, 

, 921 (6th Cir. 2004); United States v. Grier, 

, 215 (3d Cir. 2003); United States v. Gresham, 

, 261–62 (5th Cir.
1997); United States v. Dodge, 

, 145–46 (2d Cir. 1995); United States v.
Aiken, 

, 449–50 (4th Cir. 1992); United States v. Giannini, 

, 148 (9th Cir. 1972).

                                           21
      2. Does the National Firearms Act Comport with the Second
         Amendment?

      Cox and Kettler next challenge the NFA on the ground that it violates the

Second Amendment. Both contend that their NFA convictions stem from activities

that the Second Amendment protects—possessing short-barreled rifles and making,

selling, transferring, and possessing silencers—yet their challenges then diverge.

While Cox urges us to follow District of Columbia v. Heller, 

, 595, 626

(2008), and to apply means–end scrutiny to the NFA, Kettler argues that under Cox v.

New Hampshire, 

, 577 (1941), and Murdock v. Pennsylvania, 

, 113 (1943), the NFA impermissibly taxes the exercise of his constitutional right

to bear arms.

      We begin, as Cox suggests, with Heller, tracing the scope of the Second

Amendment and asking whether it permits the NFA regulations at issue. Then we

turn to Kettler’s argument and consider the impact of the Cox–Murdock rule on our

analysis.

                a. The Scope of the Second Amendment under Heller

      “A well regulated Militia, being necessary to the security of a free State, the

right of the people to keep and bear Arms, shall not be infringed.” U.S. Const.

amend. II. This amendment confers an individual right to keep and carry arms, but

that doesn’t mean that it gives everyone the absolute right to carry any weapon, in

any manner, for any purpose. 

, 626.




                                          22
      The right to keep and carry arms, like other constitutional guarantees, has

limits, and in Heller, the Court identified two venerable ones. See 

626–27.

First, since the nineteenth century, the Second Amendment has coexisted with a

range of firearms regulations. 

& n.26. Heller refused “to cast doubt on

longstanding prohibitions on the possession of firearms by felons and the mentally

ill, or laws forbidding the carrying of firearms in sensitive places such as schools and

government buildings, or laws imposing conditions and qualifications on the

commercial sale of arms.” 

Second, the Court reasoned that “the

historical tradition of prohibiting the carrying of dangerous and unusual weapons”

supported limiting the Second Amendment’s protection to weapons “in common use

at the time” of ratification. 

(internal quotation marks and citations omitted)

(quoting United States v. Miller, 

, 179 (1939)). That means, according to

Heller, that “those weapons not typically possessed by law-abiding citizens for

lawful purposes”—short-barreled shotguns, for instance—fall outside the scope of

the amendment. 

see also 

(“[W]e cannot say that

the Second Amendment guarantees the right to keep and bear [a short-barreled

shotgun].”).

      Yet within these limits, the Second Amendment takes some firearm regulations

“off the [constitutional] table.” 

. The law at issue in Heller,

the District of Columbia’s total ban on handgun possession in the home, represents

the archetype of an unconstitutional firearm regulation. See 

The law

not only prohibited “an entire class of ‘arms’” that Americans “overwhelmingly”

                                           23
choose to keep and to use for “the core lawful purpose of self-defense,” but it

extended that prohibition “to the home, where the need for defense of self, family,

and property is most acute.” 

630. Such a ban, Heller concluded, “would

fail constitutional muster” no matter what level of scrutiny the Court applied. 

& 628 n.27. Heller thus highlighted some traits of an unconstitutional

regulation, but it left open how future courts should sort the constitutional from the

unconstitutional.

      As Cox points out though, our decision in United States v. Reese interpreted

Heller to “‘suggest[] a two-pronged approach to Second Amendment challenges’ to

federal statutes.” 

, 800 (10th Cir. 2010) (quoting United States v.

Marzzarella, 

, 89 (3d Cir. 2010), and citing United States v. Skoien, 

, 641–42 (7th Cir. 2010) (en banc)). Under the two-pronged approach, the

reviewing court first asks: Does the challenged law burden conduct within the scope

of the Second Amendment’s guarantee? 

614 F.3d at 89). If

not, then the inquiry ends there. 

(quoting 

).

But if the law burdens protected conduct, then “[the court] must evaluate the law

under some form of means-end scrutiny.” 

(alteration in original) (quoting

). The law is constitutional only if it survives that

scrutiny. 

614 F.3d at 89).

      We agree with Cox that Reese’s two-pronged approach provides a workable

means of evaluating his Second Amendment challenges to the NFA’s regulation of

(1) short-barreled rifles, (2) silencers, and (3) the making and selling of firearms. We

                                           24
thus begin by asking whether each regulated activity falls within the scope of the

Second Amendment’s guarantee. See 

–01. (If we answer

“yes,” then we will address whether the NFA’s regulation of that activity survives

means–end scrutiny. 

.)

                   i.   Short-barreled rifles

      Cox argues that because short-barreled rifles are neither unusual nor especially

dangerous, possessing them falls within the Second Amendment’s ambit. He asserts

that legal uses of short-barreled rifles include “collecting, hunting, and home

defense.” Cox’s Opening Br. at 48. And when it comes to the risk of violence, Cox

claims that compared to all rifles (short- or long-barreled), “non-restricted pistols are

far more commonly used in firearm-related crime.” 

(quoting James A.

D’Cruz, Half-Cocked: The Regulatory Framework of Short-Barrel Firearms, 40

Harv. J.L. & Pub. Pol’y 493, 518 & n.161 (May 2017)).

      That handguns may bear a higher correlation to crime than rifles do, however,

implies nothing about whether short-barreled rifles, in particular, are dangerous and

unusual. More telling is Heller’s conclusion that short-barreled shotguns—close

analogues to short-barreled rifles—belong in that category of weapons not typically

possessed by law-abiding citizens for lawful purposes and, therefore, not protected

by the Second 

–25 (discussing 

);

accord United States v. Artez, 290 F. App’x 203, 208 (10th Cir. 2008) (noting that

Heller expressly foreclosed Artez’s argument that the Second Amendment protected

his possession of a sawed-off shotgun). And since Heller, many courts have

                                           25
explained that a long gun with a shortened barrel is both dangerous, because “its

concealability fosters its use in illicit activity,” and unusual, “because of its

heightened capability to cause damage.” 

; see also, e.g.,

United States v. Amos, 

, 531 (6th Cir. 2007) (McKeague, J., dissenting)

(“[A] sawed-off shotgun can be concealed under a large shirt or coat. . . . [T]he

combination of low, somewhat indiscriminate accuracy, large destructive power, and

the ability to conceal . . . makes a sawed-off shotgun useful for only violence against

another person, rather than, for example, against sport game.”).

       Though these cases dealt with short-barreled shotguns, rather than short-

barreled rifles, Cox has offered no meaningful distinction between the two. We need

not opine on whether a sufficient factual record could be developed to distinguish short-

barreled rifles from short-barreled shotguns. On the record and argument before us, we

take our cue from Heller and conclude that the possession of short-barreled rifles

falls outside the Second Amendment’s guarantee.

                   ii.   Silencers

       Next, we turn to silencers, which both Cox and Kettler contend merit Second

Amendment protection. They argue that silencers are in common use (more common,

says Kettler, than handguns were in the District of Columbia when the Court decided

Heller) and that they’re very rarely used to commit crimes—“except on television

and in the movies.” Kettler’s Opening Br. at 34. Further, they claim that silencers

protect the shooter’s (and bystanders’) hearing and, “by reducing muzzle flinch and

the disorientation that can follow a loud shot,” can improve accuracy. Cox’s Opening

                                            26
Br. at 45. And because the alternative—donning earmuffs—takes up precious time

and suppresses surrounding sounds, they argue that these hearing-protection and

accuracy benefits make silencers particularly valuable for “the core lawful purpose of

home defense.” See 

.

       But a more basic question remains: Even if silencers are commonly used by

law-abiding citizens for lawful purposes, are they a type of instrument protected by

the Second Amendment? According to Heller, “the Second Amendment extends,

prima facie, to all instruments that constitute bearable 

(emphasis added). An instrument need not have existed at the time of the founding to

fall within the amendment’s ambit, but it must fit the founding-era definition of an

“Arm[].” 

(citing two dictionaries from the eighteenth, and one from the

nineteenth, century). Then and now, that means, the Second Amendment covers

“[w]eapons of offence, or armour of defence,” or “any thing that a man wears for his

defence, or takes into his hands, or useth in wrath to cast at or strike another.” 

(alteration in original) (citations omitted). A silencer is a firearm accessory; it’s

not a weapon in itself (nor is it “armour of defence”). Accordingly, it can’t be a

“bearable arm” protected by the Second Amendment.13


       13
          Though we needn’t decide the issue, we note that the government cites
authority concluding that silencers are dangerous and unusual, the type of “arm”
traditionally excluded from the Second Amendment’s protection. See, e.g., United
States v. McCartney, 357 F. App’x 73, 76 (9th Cir. 2009) (finding silencers even
more dangerous than machineguns, for “[s]ilencers . . . are not ‘typically possessed
by law-abiding citizens for lawful purposes,’ and are less common than either short-
barreled shotguns or machine guns” (quoting 

)); United States

                                            27
      Thus, because silencers are not “bearable arms,” they fall outside the Second

Amendment’s guarantee.

                 iii.   Making and selling firearms

      Finally, Cox argues that the Second Amendment protects the making and

selling of silencers. For two reasons, however, we disagree.

      As a threshold matter, Heller endorsed “laws imposing conditions and

qualifications on the commercial sale of arms” as one of the limitations on the right

to bear 

–27. The NFA’s requirements that firearms dealers and

manufacturers register and pay taxes annually fit neatly into that category of

“presumptively lawful regulatory measures.” 

n.26; see 26 U.S.C. §§ 5801

(imposing an annual tax of $500 to $1,000 on “every importer, manufacturer, and

dealer in firearms”), 5802 (requiring “each importer, manufacturer, and dealer in

firearms” to register every year with the Secretary of the Treasury). Those

requirements, therefore, don’t infringe the right to bear arms.




v. Garnett, 

, at *4 (E.D. Mich. 2008) (concluding that “nothing in
[Heller] . . . casts doubt on the constitutionality of” the NFA’s regulation of
silencers); see also Eugene Volokh, Implementing the Right to Keep and Bear Arms
for Self-Defense: An Analytical Framework and a Research Agenda, 56 UCLA L.
Rev. 1443, 1489 & n.187 (2009) (“Bans on silencers . . . would . . . likely be
constitutional because they don’t materially burden self-defense.” (citing People v.
Brown, 

, 246–47 (Mich. 1933) (upholding a ban on silencers, among
other weapons, because the ban focused on “a partial inventory of the arsenal of the
‘public enemy,’ the ‘gangster’”; it didn’t include “weapons usually relied upon by
good citizens for defense or pleasure”)).

                                           28
       More importantly, though, the indictment charged Cox with, and the jury

found him guilty of, engaging in business as a dealer or manufacturer of silencers in

violation of the NFA. And as we’ve already concluded, the right to bear arms doesn’t

extend to silencers. Even if the Second Amendment covers the right to buy and sell

arms in the abstract, it can’t in practice protect the right to buy and sell instruments,

such as silencers, that fall outside its ambit. Thus, as they apply to Cox in particular,

the NFA’s taxation and registration requirements for firearms manufacturers and

dealers don’t burden protected conduct.

                                     *      *      *

       In sum, the Second Amendment protects neither (1) short-barreled rifles, nor

(2) silencers, nor (3) the business of manufacturing and dealing in silencers, so the

NFA’s regulation of these activities doesn’t burden protected conduct. Our analysis

thus ends at its first step, and we needn’t test the challenged regulations under any

form of means–end scrutiny. See 

–01.

              b. Applying the Rule of Cox v. New Hampshire and Murdock v.
                 Pennsylvania to Second Amendment Rights

       For the first time on appeal, Cox and Kettler urge us to find that NFA taxes

violate the Second Amendment by “impos[ing] a charge for the enjoyment of a right

granted by the federal constitution.” 

. Under Murdock and

Cox, seminal cases in the Court’s “fee jurisprudence,” the government may collect a

fee to defray administrative and maintenance costs associated with the exercise of a

constitutional (usually First Amendment) right, but it can’t impose a general revenue


                                            29
tax on the exercise of such a right. Compare 

(striking

down a license tax on the exercise of the First Amendment right to free speech), with

–77 (upholding a parade-licensing fee that the state charged “to

meet the expense incident to the administration of [the parade] and to the

maintenance of the public order”).

       When they raised the Second Amendment in the district-court proceedings,

neither Cox nor Kettler cited the Court’s fee jurisprudence, so the government urges

us to review this argument for plain error. But it doesn’t matter whether we review

for plain error or not, because the district court didn’t err (plainly or otherwise) in not

applying the framework of Murdock and Cox.

       As the government notes, neither this court nor the Supreme Court has applied

Murdock or Cox in the Second Amendment context. To analyze Second Amendment

challenges to federal statutes, we have used Reese’s two-step test, borrowed from the

Third Circuit, which does not incorporate the Court’s fee jurisprudence. See 

–01 (concluding that Heller “suggests a two-pronged approach to

Second Amendment challenges,” which asks whether the challenged law burdens

protected conduct and, if so, whether it passes muster “under some form of means-

end scrutiny” (quoting 

)).

       We recognize that other circuits have imported fee-jurisprudence principles to

their Second Amendment analyses. See, e.g., Bauer v. Becerra, 

, 1225

(9th Cir. 2017) (applying the fee-jurisprudence framework and concluding that fees

supporting an extended background-check program “can fairly be considered an

                                            30
‘expense[] of policing the activities in question,’ or an ‘expense incident to . . . the

maintenance of public order in the matter licensed’” (alterations in original) (quoting

–14, and 

)); Kwong v. Bloomberg, 

, 165 (2d Cir. 2013) (deciding that “the Supreme Court’s First Amendment

fee jurisprudence provides the appropriate foundation for addressing” the plaintiffs’

challenge to a handgun-licensing fee). But this appeal isn’t the right vehicle to test

that approach in our circuit, given our conclusion that the Second Amendment covers

neither silencers nor short-barreled rifles. NFA taxes on the possession, transfer, and

manufacture of these items do not constitute “charge[s] for the enjoyment of a right

granted by the federal constitution,” so they need not be measured against

administrative costs or the expense of maintaining public order. 

.

                                      *      *      *

       For these reasons, we conclude that the NFA comports with Cox’s and

Kettler’s Second Amendment right to bear arms.

B. Kansas’s Second Amendment Protection Act

       The validity of the Second Amendment Protection Act has never been at issue

in this case, yet the statute has played an outsized role since the case began. Now on

appeal, Cox and Kettler both contend—albeit through differing theories—that the

district court reversibly erred in ruling that they couldn’t use their reliance on the

SAPA as a defense to breaking federal firearms laws. Separately and additionally,



                                            31
Kettler claims that the SAPA caused a clash between the Governor of Kansas and the

U.S. Attorney General, which led, unjustly, to his prosecution.

      The availability and scope of any defense based on the SAPA present legal

questions that we review de novo. Cf. United States v. Hernandez-Urista, 

,

83, 84 (10th Cir. 1993) (reviewing de novo whether a good-faith defense required

that the defendant’s good-faith belief be reasonable). We start our analysis with an

overview of the SAPA, and then turn to Cox’s and Kettler’s arguments.

      The SAPA spans about three pages of the Kansas Register, but its most oft-

quoted section in this appeal is § 4(a), which states,

      A personal firearm, a firearm accessory or ammunition that is
      manufactured commercially or privately and owned in Kansas and that
      remains within the borders of Kansas is not subject to any federal law,
      treaty, federal regulation, or federal executive action, including any
      federal firearm or ammunition registration program, under the authority
      of congress to regulate interstate commerce. It is declared by the
      legislature that those items have not traveled in interstate commerce. This
      section applies to a firearm, a firearm accessory or ammunition that is
      manufactured commercially or privately and owned in the state of
      Kansas.

Second Amendment Protection Act § 4(a) (codified at Kan. Stat. Ann. § 50-1204(a)).

The SAPA also:

       declares “[a]ny act, law, treaty, order, rule or regulation of the
        government of the United States” that violates the Second Amendment
        “null, void and unenforceable in the state of Kansas,” Kan. Stat. Ann.
        § 50-1206(a);

       prohibits Kansas officials from enforcing, or attempting to enforce,
        “any act, law, treaty, order, rule or regulation of the government of the
        United States regarding any personal firearm, firearm accessory or
        ammunition that is manufactured commercially or privately and


                                           32
            owned in the state of Kansas and that remains within the borders of
            Kansas,” Kan. Stat. Ann. § 50-1206(b); and,

        subjects any federal official who enforces, or tries to enforce, “any
         act, law, treaty, order, rule or regulation of the government of the
         United States regarding a firearm, a firearm accessory, or ammunition
         that is manufactured commercially or privately and owned in the state
         of Kansas and that remains within the borders of Kansas” to
         prosecution for “a severity level 10 nonperson felony,” Kan. Stat.
         Ann. § 50-1207.

       1. Is Reliance on the Second Amendment Protection Act a Defense?

       Cox and Kettler both claim (and the government doesn’t dispute) that they

understood the SAPA to insulate from federal regulation the making, possession, and

transfer of firearms within Kansas’s borders. That was a mistake—the NFA’s taxes

and registration requirements apply to all statutorily defined firearms—yet Cox and

Kettler argue that their reliance on the SAPA still provided a defense to the charges

that they violated the NFA.

       The district court permitted mention of the SAPA during trial “as part of the

res gestae of the offenses,” but it didn’t let Cox and Kettler claim reliance on the

SAPA as a defense. Cox R. vol. 1 at 194–95.14 In doing so, it relied on settled law.



       14
          Cox specifically notes that the court: (1) denied his request to introduce a
copy of the SAPA displayed in his store; (2) refused to instruct the jury that he was
raising, “as a complete defense[,] . . . that he acted in ‘good faith’ in his belief he was
following State law [the SAPA] that superseded application of the federal law”
charged in the indictment, Cox R. vol. 1 at 207; (3) instructed the jury, over his and
Kettler’s objections, that to establish the offenses of possession (26 U.S.C.
§ 5861(d)) or transfer (§ 5861(e)) of an unregistered firearm, “[t]he government
[wa]s not required to prove that the defendant knew that the firearm was not
registered or had to be registered,” Cox R. vol. 1 at 287, 290; and (4) instructed the
jury, over Cox’s and Kettler’s objections, that because the government needn’t prove

                                            33
      The NFA’s list of “[p]rohibited acts” in 26 U.S.C. § 5861 is silent regarding

violators’ mental state; the statute just makes it “unlawful for any person” to be a

firearms dealer; or to make, receive, possess, or transfer a firearm in violation of the

NFA’s registration or other provisions. Silence, though, doesn’t necessarily mean

“that Congress intended to dispense with a conventional mens rea element, which

would require that the defendant know the facts that make his conduct illegal.”

Staples v. United States, 

, 605 (1994) (citing United States v. Balint, 

, 251 (1922)). In the context of § 5861(d) in particular, which makes it

unlawful “to receive or possess” an unregistered firearm, the government must prove

that a defendant knew the features of the firearm that made it a “firearm” under the

NFA. 

A defendant need not, however, know that the firearm was

unregistered. 

(citing United States v. Freed, 

, 607–09 (1971)).

“Knowledge of whether the gun was registered is so closely related to knowledge of

the registration requirement that requiring the Government to prove the former would

in effect require it to prove knowledge of the law.” 

n.3 (Ginsburg, J.,

concurring). And as a general rule, ignorance of the law or a mistake of law is no

defense to criminal prosecution. Cheek v. United States, 

, 199 (1991);




a defendant’s knowledge of the NFA’s registration requirements, “it [wa]s not a
defense to a charge under [26 U.S.C.] § 5861 that a defendant may have believed,
based on Kansas law, that the National Firearms Act did not require registration of a
firearm,” Cox R. vol. 1 at 295.

                                           34
accord 

n.3 (Ginsburg, J., concurring) (citing 

–14 (Brennan, J., concurring)).

       That general mistake-of-law rule forecloses Cox and Kettler’s proposed

defense—that they wrongly believed, in reliance on the SAPA, that federal firearms

regulations didn’t reach their Kansas-centric activities. To be criminally liable, Cox

and Kettler didn’t need to know that their acts were “illegal, wrong, or

blameworthy.” 

(Brennan, J., concurring). But Cox and Kettler

urge us not to apply the general rule here. Something about the SAPA, they claim,

changes things. Their arguments differ enough that we address them separately.

              a. Cox’s Argument: A Due Process Problem

       Cox grounds his argument in the due-process principle that a defendant

deserves “a meaningful opportunity to present a complete defense.” Cox’s Opening

Br. at 23–24 (quoting California v. Trombetta, 

, 485 (1984)). He argues

for a limited exception, in cases like his, to the rule that ignorance of the law isn’t a

defense. If (1) “the accused’s conduct is subject to facially conflicting state and

federal laws,” and if (2) “the state law has not (yet) been held inapplicable, inferior,

or illegitimate by any court,” then, he claims, “the accused’s good-faith reliance on

the state law is a complete defense to criminal charges brought under the federal

law.” 

4.

       Cox asserts that in prior cases, the Supreme Court has endorsed similar

defenses based on notions of due process, notice, and fairness. In an appeal brought

by a different Mr. Cox, for example, the Court concluded that the Due Process Clause

                                            35
prevented the government from “convicting a citizen for exercising a privilege which

the [government] had clearly told him was available to him.” Cox v. Louisiana, 

, 571 (1965) (quoting Raley v. Ohio, 

, 426 (1959)). In Cox, “the

highest police officials of the city, in the presence of the Sheriff and Mayor,” had

told demonstrators, including Mr. Cox, that they could meet at a spot about 101 feet

from the courthouse steps, but after the demonstration (at that spot), the state

prosecuted Cox for violating a statute banning picketing “in or near” a courthouse.

571. Based on the public officials’ actions, the Court struck Cox’s

conviction, reasoning that to sustain it “would be to sanction an indefensible sort of

entrapment by the State.” 

(quoting 

); see also United

States v. Pa. Indus. Chem. Corp., 

, 657, 673–74 (1973) (allowing a

corporation to assert, as a defense to a charge of polluting a river in violation of the

Rivers and Harbors Act, that it had relied on the Army Corps of Engineers’—the

administrative agency responsible for interpreting the Act—“longstanding

administrative construction of [the Act] as limited to water deposits that impede or

obstruct navigation”).

      In this circuit, courts treat such due-process challenges as claims of entrapment

by estoppel. See United States v. Hardridge, 

, 1192 (10th Cir. 2004)

(citing 

, and 

). To win an entrapment-by-

estoppel claim, a defendant criminally prosecuted for an offense must prove (1) that a

government agent actively misled him about the state of the law defining the offense;

(2) that the government agent was “responsible for interpreting, administering, or

                                           36
enforcing the law defining the offense”; (3) that the defendant actually relied on the

agent’s misleading pronouncement in committing the offense; and (4) that the

defendant’s reliance was “reasonable in light of the identity of the agent, the point of

law misrepresented, and the substance of the misrepresentation.” 

States v. Gutierrez-Gonzalez, 

, 1167 (10th Cir. 1999), and United

States v. Nichols, 

, 1018 (10th Cir. 1994)).

      Here, Cox wouldn’t be able to prove either (1) that the misleading government

agent (the Kansas legislature) was responsible for interpreting, administering, or

enforcing the law defining the offense (the NFA) or (2) that his reliance on the

misleading pronouncement (the SAPA) was reasonable in light of the circumstances.

First, unlike the police in Cox, who enforced the anti-picketing law, or the Army

Corps of Engineers in Pennsylvania Industrial Chemical, which administered the

Rivers and Harbors Act, the Kansas legislature (which wrote the SAPA) isn’t

responsible for administering or enforcing the NFA (or any other federal law).

Second, irrespective of the government agent’s identity, the substance of the SAPA’s

misrepresentation made Cox’s reliance on it unreasonable. Section 4(a) of the SAPA

expressly states that certain firearms and accessories, if kept in Kansas, aren’t

“subject to any federal law, treaty, federal regulation, or federal executive action,

including any federal firearm or ammunition registration program, under the

authority of congress to regulate interstate commerce. It is declared by the legislature

that those items have not traveled in interstate commerce.” Kan. Stat. Ann.



                                           37
§ 50-1204(a) (emphases added). But the SAPA says nothing about laws, such as the

NFA, passed under Congress’s authority to tax.

      Cox counters that this reading of the SAPA “ignores provisions in the Act that

prohibit both state and federal actors from enforcing ‘any’ federal firearms laws or

regulations with respect to local firearms.” Cox’s Reply Br. at 2–3 (citing Kan. Stat.

Ann. §§ 50-1206(b), 1207). But Cox is wrong that “[n]o Commerce Clause limit

appears” in these provisions, which prohibit state officials from, and subject federal

officials to prosecution for, enforcing or attempting to enforce federal laws against

any firearm, accessory, or ammunition “that is manufactured commercially or

privately and owned in the state of Kansas and that remains within the borders of

Kansas.” Cox’s Reply Br. at 3; Kan. Stat. Ann. §§ 50-1206(b), 1207 (emphases

added). These provisions protect only homegrown, local firearms, so the Kansas

legislature didn’t need to utter the magic words, “Commerce Clause,” to make clear

its intent to preserve constitutional limits on the federal government’s power over

intrastate activity. Kansas wasn’t considering, and didn’t purport to limit, Congress’s

taxing-clause authority. Any other interpretation ignores the SAPA’s emphasis on the

local nature of the firearms’ (and accessories’) manufacture and ownership.

      Cox, therefore, can’t use the SAPA to establish an entrapment-by-estoppel

defense in this case. Cf. 

–96 (rejecting representations

about the application of federal firearms laws made (1) by the Kansas City Police

Department, (2) by the defendant’s state-court sentencing judge, and (3) by a licensed

federal firearms dealer as bases for an entrapment-by-estoppel defense); Gutierrez-

                                          38


–69 (denying an entrapment-by-estoppel defense based on

alleged misrepresentations made (1) by a private entity that assisted deported,

indigent aliens, because the entity wasn’t a government agency and because the

defendant’s reliance on its misrepresentations wasn’t reasonable given the

defendant’s admission that he was in the country illegally, and (2) by an immigration

official, because the defendant couldn’t reasonably form the belief that he was in the

U.S. legally merely from the official’s failure to arrest him “on the spot”).

      Nor do notions of due process warrant expanding entrapment by estoppel and

creating a new, estoppel-like defense to fit situations in which “the accused’s conduct

is subject to facially conflicting state and federal laws” and the accused acts in good-

faith reliance on the state law. Cox’s Opening Br. at 24. Nothing about a statute

makes reliance on its pronouncements more consequential than reliance on a

government agent’s non-statutory statements.15 And before we apply the doctrine of


      15
          According to Cox, “[t]he collective judgment of an entire state legislature,
regardless of jurisdiction, is surely more trustworthy than the advice of an extra-
jurisdictional individual official.” Cox’s Opening Br. at 30. But the superiority of
collective judgments is beside the point. State legislatures have no special expertise in,
and aren’t charged with enforcing, federal law. State legislators are more likely to
consider their duty to promote their constituents’ policy preferences than to expound on
the reach of federal law.
       Nor is Cox’s analogy to the Fourth Amendment context persuasive. There, the
Court has often deemed it reasonable for law-enforcement officers to rely on
legislative pronouncements in forming probable cause. See, e.g., Michigan v.
DeFillippo, 

, 38 (1979) (“The enactment of a law forecloses speculation
by enforcement officers concerning its constitutionality—with the possible exception
of a law so grossly and flagrantly unconstitutional that any person of reasonable
prudence would be bound to see its flaws.”). But whether an officer’s belief was
reasonable for probable-cause purposes is a very different question, with very

                                            39
estoppel against the government, due process requires us to weigh the needs of

society against the “natural sympathy” that we may feel toward defendants like Cox

and Kettler, who have been prosecuted for conduct that, based on a state statute’s

assurances, they believed was lawful. 

. Application of

the estoppel doctrine is justified only if it doesn’t “interfere with underlying

government policies or unduly undermine the correct enforcement of a particular law

or regulation.” United States v. Browning, 

, 702 (10th Cir. 1980) (citing

27 A.L.R. Fed. 702 (1976)). Here, though, allowing state legislatures to estop the

federal government from prosecuting its laws would upset the balance of powers

between states and the federal government and contravene the Supremacy Clause.

See U.S. Const. art. VI. We can’t countenance that result, so we decline to adopt

Cox’s proposed defense.

      Accordingly, we reject Cox’s argument that due process required that he be

able to present his reliance on the SAPA as a defense.

             b. Kettler’s Argument: Mens Rea and the Model Penal Code’s
                Approach

      Kettler, in turn, focuses on the mens rea element of possessing an unregistered

firearm (in his case, a silencer) in violation of 26 U.S.C. § 5861(d). He claims that

the “jurisdictional dispute between sovereigns” over the SAPA “demands a more




different consequences, than whether a defendant’s reliance was reasonable for
estoppel purposes. So different, in fact, that answering the former doesn’t help
answer the latter.

                                           40
thoughtful analysis of the mens rea element of 26 U.S.C. § 5861 than given by the

court below.” Kettler’s Opening Br. at 50. Because possession of an unregistered

silencer is a “morally indifferent” act (“malum prohibitum, not malum in se”), he

contends, the mens rea element should yield to a mistake-of-law defense premised on

the Model Penal Code’s approach. 

       Section 2.04(3) of the Model Penal Code, titled “Ignorance or Mistake,”

provides,

       A belief that conduct does not legally constitute an offense is a defense
       to a prosecution for that offense based upon such conduct when:

       ...

       (b) [the actor] acts in reasonable reliance upon an official statement of
       the law, afterward determined to be invalid or erroneous, contained in
       (i) a statute or other enactment; (ii) a judicial decision, opinion or
       judgment; (iii) an administrative order or grant of permission; or (iv) an
       official interpretation of the public officer or body charged by law with
       responsibility for the interpretation, administration or enforcement of the
       law defining the offense.

Model Penal Code § 2.04(3) (Am. Law Inst. 2017) (emphasis added).

       According to the explanatory note, this subsection “establishes a limited

exception to the principle . . . that culpability is not generally required as to the

illegality of the actor’s conduct.” 

Explanatory Note. But the drafters

delineated this exception “narrowly . . . so as to induce fair results without undue risk


       16
         Cox also mentions the Model Penal Code, claiming that it’s consistent with
his proposed good-faith defense. And Cox, too, argues that NFA offenses aren’t
inherently immoral, a trait that, he claims, “weighs in favor of recognizing his [good-
faith] defense.” Cox’s Opening Br. at 34. To avoid duplicating any analysis, we
address both points only once, here.

                                            41
of spurious litigation.” 

instance, § 2.04(3)(b)(iv) permits reliance on an

“official statement of the law” contained in an “official interpretation of the public

officer or body” only if the interpreting officer or body is “charged by law with

responsibility for the interpretation, administration or enforcement of the law

defining the offense.”

      Yet unlike paragraph (b)(iv) of § 2.04(3), paragraph (b)(i) does not expressly

limit the “statute[s] or other enactment[s]” on whose pronouncements a defendant

may “act in reasonable reliance.” Model Penal Code § 2.04(3)(b)(i). So, Kettler

contends, paragraph (b)(i) permits reliance on a statute (like the SAPA) regardless of

the enacting legislature’s jurisdiction, “suppl[ying] a defense directly supporting [his]

case.” Kettler’s Opening Br. at 54.

      We disagree. The drafters of the Model Penal Code’s ignorance-or-mistake-of-

law defense intended only a narrow exception in the interest of fair results. See

Model Penal Code § 2.04(3) Introductory Note. Thus, the code’s failure to restrict

reliance on statutes to those passed under the same authority as the law defining the

offense probably reflects that the drafters weren’t considering our circumstance, not

that they intended to allow state governments to estop the federal government from

enforcing its laws. After all, the plain language of the code requires “reasonable

reliance upon an official statement of the law.” 

(3)(b) (emphases added). A

state legislature’s statement about the reach of federal law is hardly an “official”

statement of federal law, and to rely on such a statement is not reasonable.



                                           42
      Ultimately, however, the Model Penal Code isn’t the law in this circuit. Like

Cox’s, Kettler’s claim sounds in this circuit’s doctrine of entrapment by estoppel. See

–68. And we’ve already concluded, in resolving

Cox’s claim, that reliance on the SAPA can’t sustain an entrapment-by-estoppel

defense in these cases. 

Section B.1.a. It’s fatal to their proposed defense

that “in light of the identity of the agent, the point of law misrepresented, and the

substance of the misrepresentation,” Cox’s and Kettler’s reliance on the SAPA was

not reasonable. 

.

      Nor does Kettler’s characterization of an NFA offense as “malum prohibitum,”

or wrong only because of a statutory proscription, justify broadening the entrapment-

by-estoppel doctrine’s (or the Model Penal Code’s) exception to the rule that a

mistake of law generally provides no defense to a criminal prosecution. Kettler’s

Opening Br. at 52. Kettler claims that “everyone knows the laws of the Creator, as

they are written in the created order and imprinted by the Creator on every man” and

that, as a result, the general mistake-of-law rule applies only to offenses that are mala

in se (inherently wrong), not mala prohibita. 

1:18–20). But he

cites no legal precedent carving out such an exception.

      In Cheek, the Court explained the general mistake-of-law rule’s provenance:

“[b]ased on the notion that the law is definite and knowable, the common law

presumed that every person knew the 

. That presumption might

not always hold true anymore given the “proliferation of statutes and regulations,”

especially in the tax context, so Congress has “softened” its impact “by making

                                            43
specific intent to violate the law an element of certain federal criminal tax offenses.”

(citing United States v. Murdock, 

(1933)). Accordingly,

Cheek recognized that since the 1930’s, the Court has interpreted the term “willfully”

in federal criminal tax statutes “as carving out an exception to the traditional rule.”

00. “Willfulness,” Cheek explained, means “the ‘voluntary, intentional

violation of a known legal duty.’” 

01 (quoting United States v. Pomponio, 

, 12 (1976)). Cheek, however, didn’t suggest that the general mistake-of-law

rule disappears whenever an offense may be categorized as malum prohibitum.

      Moreover, Congress didn’t put a “willfulness” requirement in the NFA. See 26

U.S.C. § 5861. As explained above, the NFA is silent about mens rea. The Court

filled the gap, based on the presumption that criminal liability should attach only

when a defendant knows the facts that make his conduct illegal, by requiring that the

defendant know the characteristics of a firearm that bring it within the NFA’s ambit.

. The Court took the mens-rea presumption no further,

however, “lest it conflict with the related presumption, ‘deeply rooted in the

American legal system,’ that, ordinarily, ‘ignorance of the law or a mistake of law is

no defense to criminal prosecution.’” 

n.3 (Ginsburg, J., concurring)

(quoting 

). Under Staples, then, certain factual mistakes (e.g.,

that a firearm isn’t a “firearm” for NFA purposes) may provide a defense to a charge

of violating the NFA, but legal mistakes (e.g., that the NFA doesn’t apply to locally

made firearms) do not.



                                           44
      Accordingly, we reject Kettler’s argument that the mens rea element of 26

U.S.C. § 5861 should be subject to a mistake-of-law defense like the Model Penal

Code’s.

                                     *      *      *

      Finally, we note that Cox’s and Kettler’s reliance on the SAPA did, in the end,

mitigate their sentences, if not their guilt. At the sentencing hearing, the court

reasoned that even though the SAPA wasn’t available as a defense at trial, the court

could “take [it] into account” in deciding to impose probationary, instead of prison,

sentences. Cox R. vol. 3 at 716:14–15. Speaking to Cox and Kettler, the court said, “I

believe that you both honestly felt that you were protected by [the SAPA] and I

believe that to be so[.]” 

Thus, the court continued, “I am giving you

what benefit I can of that statute here at sentencing.” 

That benefit

turned out to be two years’ probation for Kettler and one year’s for Cox. (The NFA

allows for a penalty of up to ten years in prison, a fine of up to $10,000, or both for

violating any of its provisions. 26 U.S.C. § 5871.)

      For all these reasons, we conclude that the district court was correct to prohibit

Cox and Kettler from introducing their reliance on the SAPA as a defense to their

NFA charges. Cox and Kettler received a fair trial and, at sentencing, the benefit of

their good-faith reliance on the SAPA, so we see no reason—be it grounded in

notions of due process or premised on presumptions about mens rea—either to create

a new defense out of whole cloth (as Cox suggests) or to borrow one from the Model

Penal Code (as Kettler suggests).

                                           45
       2. Was Kettler “Snared in a Constitutional Dispute Between Two
          Independent but Interrelated Civil Sovereigns”?

       In a related argument, Kettler contends that the political rumpus following the

SAPA’s enactment “snared [him] in a constitutional dispute between two

independent but interrelated civil sovereigns.” Kettler’s Opening Br. at 36. Citing the

Declaration of Independence and its protection of unalienable rights, he argues that

“[w]henever any government becomes destructive of those rights, it is the duty of the

people—through their lower civil magistrates—to resist the misuse of power even to

the point of taking up arms against tyranny as America’s founders did in 1776.” 

(footnote omitted). Contrary to the founders’ federalist ideals, Kettler claims

that after passing the SAPA, Kansas’s resolve weakened. “In a deferential, not

confrontational, letter,” he notes, the Kansas Attorney General asked the U.S.

Attorney General either to order the dismissal of the indictment or to support a

presidential pardon. 

But Kettler claims that he deserves more than clemency

or a pardon—“[h]e deserves the protection of the republican form of government

established in Kansas at the time of its admission to the union so that he is not

punished for being caught between the two sovereigns to which he oversees

allegiance.” 

       We’re unable to give Kettler either as an appellate remedy. The Constitution

created the “judicial Power” to resolve cases and controversies, U.S. Const. art. III,

§ 2, cl. 1, and to do so, we have jurisdiction “of appeals from all final decisions of the

district courts,” 28 U.S.C. § 1291. As Chief Justice Marshall wrote, “the essential


                                           46
criterion of appellate jurisdiction” is “that it revises and corrects the proceedings in a

cause already instituted, and does not create that cause.” Marbury v. Madison, 5 U.S.

(1 Cranch) 137, 175 (1803). Yet in making his argument, Kettler points to no error in

the district-court proceedings. Without such a claim, we can’t simply order the

executive branch to grant Kettler clemency or demand that Kansas grant him the

protection of a republican form of government. Stated otherwise, to fulfill the

judiciary’s duty “to say what the law is,” we need a legal question. 

      Accordingly, we decline to grant Kettler relief for being “snared in a

constitutional dispute” between Kansas and the federal government. Kettler’s

Opening Br. at 36.

                                    CONCLUSION

      For these reasons, we affirm the judgments of the district court.




                                            47
17-3034, United States v. Cox
17-3035, United States v. Kettler

HARTZ, Circuit Judge, concurrence

      I join Judge Phillips’s opinion in full. I add this comment solely to caution against

overreading our holding regarding silencers. In determining that silencers are not

protected by the Second Amendment, we explain that they are not “bearable arms.” We

had no occasion to consider whether items that are not themselves bearable arms but are

necessary to the operation of a firearm (think ammunition) are also protected.