RECOMMENDED FOR FULL-TEXT PUBLICATION
                             Pursuant to Sixth Circuit I.O.P. 32.1(b)
                                    File Name: 19a0205p.06

                  UNITED STATES COURT OF APPEALS
                                FOR THE SIXTH CIRCUIT



 CHRISTA GAIL PIKE,                                    ┐
                               Petitioner-Appellant,   │
                                                       │
                                                        >      No. 16-5854
       v.                                              │
                                                       │
                                                       │
 GLORIA GROSS, Warden,                                 │
                              Respondent-Appellee.     │
                                                       ┘

                         Appeal from the United States District Court
                    for the Eastern District of Tennessee at Chattanooga.
                  No. 1:12-cv-00035—Harry S. Mattice, Jr., District Judge.

                                 Argued: October 17, 2018

                            Decided and Filed: August 22, 2019

                 Before: COOK, GRIFFIN, and STRANCH, Circuit Judges.
                                _________________

                                        COUNSEL

ARGUED:       Stephen A. Ferrell, FEDERAL DEFENDER SERVICES OF EASTERN
TENNESSEE, INC., Knoxville, Tennessee, for Appellant. Richard D. Douglas, OFFICE OF
THE TENNESSEE ATTORNEY GENERAL, Nashville, Tennessee, for Appellee. ON BRIEF:
Stephen A. Ferrell, FEDERAL DEFENDER SERVICES OF EASTERN TENNESSEE, INC.,
Knoxville, Tennessee, for Appellant. Jennifer L. Smith, OFFICE OF THE TENNESSEE
ATTORNEY GENERAL, Nashville, Tennessee, for Appellee.

        GRIFFIN, J., delivered the opinion of the court in which COOK and STRANCH, JJ.,
joined. STRANCH, J. (pp. 15–18), delivered a separate concurring opinion.
 No. 16-5854                               Pike v. Gross                                   Page 2


                                       _________________

                                            OPINION
                                       _________________

       GRIFFIN, Circuit Judge.

       Petitioner Christa Gail Pike, a Tennessee death-row inmate, appeals the district court’s
denial of her petition for habeas corpus under 28 U.S.C. § 2254. Because we conclude that the
state court’s determination that she is unable to establish prejudice on her claims of ineffective
assistance of counsel during the penalty phase of her capital trial was not an unreasonable
application of clearly established federal law, we affirm.

                                                 I.

                                                 A.

       This case began with the horrific and brutal 1995 murder of Colleen Slemmer. Pike and
Slemmer were both students at the Job Corps Center in Knoxville, Tennessee at the time. State
v. Pike, 

, 907–08 (Tenn. 1998). They had a strained relationship; Pike claimed
that Slemmer “had been ‘trying to get [her] boyfriend’ and . . . ‘running her mouth’ everywhere.”

These bad feelings unfortunately resulted in the following events, as the Tennessee
Supreme Court explained in a detailed opinion:

       [O]n January 11, 1995, [Pike], a student at the Job Corps Center in Knoxville, told
       her friend Kim Iloilo, who was also a student at the facility, that she intended to
       kill another student, Colleen Slemmer, because she “had just felt mean that day.”
       The next day, January 12, 1995, at approximately 8:00 p.m., Iloilo observed Pike,
       along with Slemmer, and two other Job Corps students, Shadolla Peterson and
       Tadaryl Shipp, Pike’s boyfriend, walking away from the Job Corps center toward
       17th Street. At approximately 10:15 p.m., Iloilo observed Pike, Peterson, and
       Shipp return to the Center. Slemmer was not with them.
       Later that night, Pike went to Iloilo’s room and told Iloilo that she had just killed
       Slemmer and that she had brought back a piece of the victim’s skull as a souvenir.
       Pike showed Iloilo the piece of skull and told her that she had cut the victim’s
       throat six times, beaten her, and thrown asphalt at the victim’s head. Pike told
       Iloilo that the victim had begged “them” to stop cutting and beating her, but Pike
       did not stop because the victim continued to talk. Pike told Iloilo that she had
       thrown a large piece of asphalt at the victim’s head, and when it broke into
 No. 16-5854                              Pike v. Gross                                  Page 3


       smaller pieces, she had thrown those at the victim as well. Pike told Iloilo that a
       meat cleaver had been used to cut the victim’s back and a box cutter had been
       used to cut her throat. Finally, Pike said that a pentagram had been carved onto
       the victim’s forehead and chest. Iloilo said that Pike was dancing in a circle,
       smiling, and singing “la, la, la” while she related these details about the murder.
       When Iloilo saw Pike at breakfast the next morning she asked Pike what she had
       done with the piece of the victim’s skull. Pike replied that it was in her pocket
       and then said, “And, yes, I’m eating breakfast with it.”
       During a class later that morning, Pike made a similar statement to Stephanie
       Wilson, another Job Corps student. Pike pointed to brown spots on her shoes and
       said, “that ain’t mud on my shoes, that’s blood.” Pike then pulled a napkin from
       her pocket and showed Wilson a piece of bone which Pike said was a piece of
       Slemmer’s skull. Pike also told Wilson that she had slashed Slemmer’s throat six
       times and had beaten Slemmer in the head with a rock. Pike told Wilson that the
       victim’s blood and brains had been pouring out and that she had picked up the
       piece of skull when she left the scene.

       None of Pike’s friends or colleagues reported the crime to the police, but a University of
Tennessee Grounds Department employee nonetheless found Slemmer’s body on January 13. 

That employee later “testified that the body was so badly beaten that he had first
mistaken it for the corpse of an animal,” before realizing it was a human female when he saw the
victim’s clothes and her exposed breast. 

police quickly discovered Pike’s
connection to the crime and interviewed her on January 14. 

Pike waived her Miranda
rights and gave a complete statement to the police about her involvement in the murder. As
recounted by the Tennessee Supreme Court:

       Pike claimed that she had not planned to kill Slemmer, but she had instead
       planned only to fight Slemmer and let her know “to leave me the hell alone.”
       However, Pike admitted that she had taken a box cutter and a miniature meat
       cleaver with her when she and the victim left the Job Corps Center. Pike said she
       had borrowed the miniature meat cleaver, but refused to identify the person who
       had loaned it to her.
       According to Pike, she asked Slemmer to accompany her to the Blockbuster
       Music Store, and as they were walking, Pike told Slemmer that she had a bag of
       “weed” hidden in Tyson Park. Though Pike refused to name the other parties
       involved in the incident, she said the group began walking toward the [University
       of Tennessee] campus. Upon arriving at the steam plant on [the University of
       Tennessee]’s agricultural campus, Pike and Slemmer exchanged words. Pike then
No. 16-5854                             Pike v. Gross                                    Page 4


     began hitting Slemmer and banging Slemmer’s head on her knee. Pike threw
     Slemmer to the ground and kicked her repeatedly. According to Pike, as she
     slammed Slemmer’s head against the concrete, Slemmer repeatedly asked, “Why
     are you doing this to me?” When Slemmer threatened to report Pike so she would
     be terminated from the Job Corps program, Pike again repeatedly kicked Slemmer
     in the face and side. Slemmer lay on the ground and cried for a time and then
     tried to run away, but another person with Pike caught Slemmer and pushed her to
     the ground.
     Pike and the other person, who Pike referred to as “he,” held Slemmer down until
     she stopped struggling, then dragged her to another area where Pike cut
     Slemmer’s stomach with the box cutter. As Slemmer “screamed and screamed,”
     Pike recounted how she began to hear voices telling her that she had to do
     something to prevent Slemmer from telling on her and sending her to prison for
     attempted murder.
     At this point Pike said she was just looking at Slemmer and “just watching her
     bleed.” When Slemmer rolled over, stood up and tried to run away again, Pike
     cut Slemmer’s back, “the big long cut on her back.” Pike said Slemmer
     repeatedly tried to get up and run. Pike recounted how Slemmer bargained for her
     life, begging Pike to talk to her and telling Pike that if she would just let her go,
     she would walk back to her home in Florida without returning to the Job Corps
     facility for her belongings. Pike told Slemmer to “shut up” because it “was harder
     to hurt somebody when they’re talking to you.” Pike said the more Slemmer
     talked, the more she kicked Slemmer in the face.
     Slemmer asked Pike what she was going to do to her, at which point Pike thought
     she heard a noise. Pike left the scene to check out the surrounding area to make
     sure no one was around. When she returned, Pike began cutting Slemmer across
     the throat. When Slemmer continued to talk and beg for her life, Pike cut
     Slemmer’s throat several other times. Pike said that Slemmer continued to talk
     and tried to sit up even though her throat had been cut several times, and that Pike
     and the other person would push her back on the ground.
     Slemmer attempted to run away again, and Pike threw a rock which hit Slemmer
     in the back of the head. Pike stated that “the other person” also hit Slemmer in
     the head with a rock. When Slemmer fell to the ground, Pike continued to hit her.
     Eventually Pike said she could hear Slemmer “breathing blood in and out,” and
     she could see Slemmer “jerking,” but Pike “kept hitting her and hitting her and
     hitting her.” Pike eventually asked Slemmer, “Colleen, do you know who’s doing
     this to you?” Slemmer’s only response was groaning noises. At this point, Pike
     said she and the other person each grabbed one of Slemmer’s feet and dragged her
     to an area near some trees, leaving her body on a pile of dirt and debris. They left
     Slemmer’s clothing in the surrounding bushes. Pike said the episode lasted “for
     about thirty minutes to an hour.” Pike admitted that she and the other person had
     forced the victim to remove her blouse and bra during the incident to keep
     Slemmer from running away. Pike also admitted that she had removed a rag from
 No. 16-5854                               Pike v. Gross                                   Page 5


       her hair and tied it around Slemmer’s mouth at one point to prevent Slemmer
       from talking. Pike denied carving a pentagram in the victim’s chest, but said that
       the other person had cut the victim on her chest.

                                                B.

       The state of Tennessee prosecuted Pike for Slemmer’s murder. At trial, much of Pike’s
unsuccessful defense centered on her mental health. Dr. Eric Engum testified that he had
examined Pike and, although she suffered from no symptoms of brain damage or insanity, she
did suffer from “very severe borderline personality disorder” and exhibited signs of cannabis
dependence and a depressive disorder. On this basis, Dr. Engum testified that, while there was
no question Pike killed Slemmer, it was his opinion that she did not act with deliberation or
premeditation and simply lost control, consistent with Pike’s diagnosis of borderline personality
disorder. Additionally, Dr. William Bernet, a forensic psychiatrist with a specialty in satanic
rituals, testified that he reviewed Pike’s statements and the medical/psychological reports
prepared by the other professionals involved in the case, and concluded that though the crime
had “satanic elements,” it appeared more indicative of “an adolescent dabbling in Satanism.” He
also discussed the phenomenon of collective aggression, in which a group of people become
emotionally aroused and “the end result is that they engage in some kind of violent, extremely
violent activity.”   It was his opinion that Slemmer’s murder was consistent with that
phenomenon.

       The jury convicted Pike of premeditated first-degree murder and conspiracy to commit
first-degree murder under Tennessee law. The Tennessee trial judge sentenced Pike to twenty-
five years’ imprisonment on the conspiracy conviction and held a sentencing hearing to allow the
jury to determine whether to sentence Pike to death for the murder conviction. Pike’s attorney,
William Talman, originally intended to rely solely on the testimony of Dr. Diana McCoy, a
mitigation expert hired by the defense. But shortly before the sentencing hearing, Talman
switched his plan and called only Pike’s aunt, father, and mother. All three testified about Pike’s
difficult childhood, and her exhibition of behavioral problems throughout her adolescence.
Ultimately, the jury sentenced Pike to death by electrocution, finding that “[t]he murder was
 No. 16-5854                                Pike v. Gross                                  Page 6


especially heinous, atrocious or cruel in that it involved torture or serious physical abuse beyond
that necessary to produce death,” and “[t]he murder was committed for the purpose of avoiding,
interfering with or preventing a lawful arrest or prosecution of the defendant or another.” See
Tenn. Code Ann. § 39–13–204(i)(5), (6) (listing aggravating circumstances a jury must find to
sentence a person to death).

       Pike appealed her convictions and sentences, but both the Tennessee Court of Criminal
Appeals, State v. Pike, No. 03C01-CR-00408, 

, at *1 (Tenn. Crim. App. 1997),
and the Tennessee Supreme Court, 

, affirmed. Pike then filed a petition
for postconviction relief in the state trial court.      The postconviction court denied relief,
concluding as relevant to this appeal that Pike’s trial counsel was not ineffective for failing to
present alternative expert testimony or additional lay testimony on compelling mitigation in her
life history.   The Tennessee Court of Criminal Appeals affirmed the denial of Pike’s
postconviction petition. Pike v. State, No. E2009-00016-CCA-R3-PD, 

, at *1
(Tenn. Crim. App. 2011). The Tennessee Supreme Court denied her application for permission
to appeal, 

United States Supreme Court denied certiorari, Pike v. Tennessee, 

(2012).

                                                 C.

       This habeas petition followed. Pike argues that her trial counsel was ineffective during
the penalty phase of trial for failing to present mitigating evidence he discovered during the
investigation and for failing to discover other relevant and compelling mitigating evidence,
among other reasons. The parties filed cross-motions for summary judgment, and the district
court held a two-day evidentiary hearing on Pike’s petition and the parties’ motions. The district
court granted respondent’s motion for summary judgment and dismissed Pike’s habeas petition.
We granted her a limited certificate of appealability, restricted to whether she received
ineffective assistance of counsel during the penalty phase of her trial.

                                                 II.

       “In an appeal from the denial of habeas relief, we review the district court’s legal
conclusions de novo and its factual findings for clear error.” Scott v. Houk, 

, 503
 No. 16-5854                               Pike v. Gross                                   Page 7


(6th Cir. 2014). Under the Antiterrorism and Effective Death Penalty Act of 1996 (AEDPA), we
may only overturn a state conviction for an issue adjudicated on the merits if it (1) “was contrary
to, or involved an unreasonable application of, clearly established Federal law, as determined by
the Supreme Court of the United States;” or (2) “was based on an unreasonable determination of
the facts in light of the evidence presented” to the state court. 28 U.S.C. § 2254(d). A claim for
habeas relief based on the “unreasonable application” prong must show more than that the state
court’s ruling was merely incorrect—“an unreasonable application of federal law is different
from an incorrect application of federal law.” Harrington v. Richter, 

, 101 (2011)
(quoting Williams v. Taylor, 

, 410 (2000)). Indeed, “[a] state court’s determination
that a claim lacks merit precludes federal habeas relief so long as ‘fairminded jurists could
disagree’ on the correctness of the state court’s decision.” 

v. Alvarado,

, 664 (2004)). “This is a difficult to meet and highly deferential standard for
evaluating state-court rulings, which demands that state-court decisions be given the benefit of
the doubt.” Cullen v. Pinholster, 

, 181 (2011) (internal quotation marks and
citations omitted).

                                                III.

       As in all cases alleging ineffective assistance of counsel, we turn to Strickland v.
Washington’s two-part framework: a criminal defendant claiming ineffective assistance must
prove that (1) counsel’s performance was objectively unreasonable, and (2) the deficient
performance actually prejudiced the defense. 

, 687 (1984). Because a party
alleging that claim has the burden of proof on both prongs and her failure on either thwarts relief,
we can address an ineffective-assistance claim in any order we choose. See Smith v. Spisak,

, 151 (2010) (assuming deficient performance but denying relief for lack of
prejudice).

       In this case, “[w]e choose to focus on the prejudice prong of the Strickland test because it
is easier to resolve, and there can be no finding of ineffective assistance of counsel without
prejudice.” Phillips v. Bradshaw, 

, 216 (6th Cir. 2010) (citation omitted). Under
Strickland’s prejudice prong, “[t]he defendant must show that there is a reasonable probability
that, but for counsel’s unprofessional errors, the result of the proceeding would have been
 No. 16-5854                              Pike v. Gross                                   Page 8

. Put differently, Pike bears the burden of showing that a reasonable
probability exists that, but for counsel’s deficient performance, the jury would have selected a
different sentence. Wong v. Belmontes, 

, 19–20 (2009) (per curiam).

        Counsel’s failure to either present mitigating evidence at sentencing, 

–96, or discover all reasonably available mitigating evidence, Wiggins v. Smith, 

, 521–24 (2003), can support a finding of ineffective assistance. But “the failure to present
additional mitigating evidence that is ‘merely cumulative’ of that already presented does not rise
to the level of a constitutional violation.” Broom v. Mitchell, 

, 410 (6th Cir. 2006).
“[T]he new evidence that a habeas petitioner presents must differ in a substantial way—in
strength and subject matter—from the evidence actually presented at sentencing.” Clark v.
Mitchell, 

, 286 (6th Cir. 2005) (quoting Hill v. Mitchell, 

, 319 (6th Cir.
2005)); see also Sears v. Upton, 

, 954 (2010) (per curiam) (“[T]here is no prejudice
when the new mitigating evidence ‘would barely have altered the sentencing profile presented’
to the decisionmaker . . . .”).

        Pike’s claim really presents two separate issues. First, she argues that her trial counsel
was ineffective for failing to present the testimony of her mitigation expert, Dr. McCoy, at her
sentencing hearing. Second, she contends that counsel was ineffective for failing to discover
other compelling mitigation evidence, such as Pike’s organic brain damage, bipolar disorder,
post-traumatic stress disorder, and lay witnesses who could have provided a more-complete
picture of Pike’s humanity.

                                                A.

        Turning first to Dr. McCoy, it is unclear what substantially different mitigating evidence
she would have offered by way of her testimony and the “social history” that she prepared of
Pike. Dr. McCoy’s social history provided an extensive examination of Pike’s entire life and
explained many of the life events and childhood difficulties that led her to the murder. For
example, Dr. McCoy’s report notes that “[i]t ha[d] been suggested that [the boyfriend of Pike’s
grandmother] may have sexually abused [Pike]” as a child, though other members of Pike’s
family, including her father, questioned the truthfulness of that accusation. The social history
 No. 16-5854                                Pike v. Gross                                 Page 9


also noted that Pike’s mother had a number of boyfriends and relationships in Pike’s youth, with
many of the men treating Pike in an abusive or sexually inappropriate manner. But, again, Pike’s
accusations were met with doubt and outright opposition by members of her family. The social
history also noted that Pike believed her paternal grandmother was the only person that ever
loved her, was inconsolable for days after her grandmother’s death, and actually attempted
suicide for the first time after her grandmother passed away. In sum, the social history laid out
an upbringing of substantial difficulty and strife.

       While that “social history” document was certainly thorough, and we will assume for the
sake of argument that Dr. McCoy would have been able to testify consistently with the evidence
she accumulated and compiled therein, the jury already got much of the social history’s general
content during the penalty phase of the trial. Pike’s mother, Carissa Hansen, testified that Pike
spent much of her childhood with her paternal grandmother because neither Hansen nor her
husband were ever really home. Hansen testified that she was a drug abuser and heavy drinker
during Pike’s childhood, which also contributed to Pike spending time with her grandmother.
Hansen also testified that Pike first attempted suicide after her grandmother’s death in 1988, but
that Hansen had not gotten her much psychiatric or psychological help in the aftermath. At least
once Hansen chose one of her husbands over Pike, sending Pike away when there was conflict
between them. She also admitted to smoking marijuana both in front of and, on at least one
occasion, with Pike during her teenage years. On cross-examination, Hansen testified that when
Pike was twelve years old she threatened one of Hansen’s boyfriends with a butcher knife and
that Pike had been a troubled child for years. But Hansen did state that Pike’s “troubles” were
Hansen’s fault, and she blamed herself for Pike’s behavior.

       Pike’s father, Glenn Pike, also testified on her behalf. Glenn admitted rejecting Pike
during her childhood and telling her that she could no longer come to his home where he lived
with a new wife and family. He testified that he had picked his new wife and children over Pike
and sent her away when there was conflict between them. He testified that, another time, he
kicked Pike out of his home for doing poorly in school. And yet another time Glenn “rejected”
Pike and even signed adoption papers to allow her to be adopted, though this was shortly before
her eighteenth birthday and an adoption never came to fruition.
 No. 16-5854                               Pike v. Gross                                 Page 10


       Pike’s aunt, Carrie Ross, also testified. Ross noted that Pike’s care and upbringing fell
mostly on the shoulders of her paternal grandmother and that the two were inseparable. She
noted that Pike’s childhood home was constantly filthy to the point that Pike, as a baby, would
be “crawling around through piles of dog stool all over the house.” Ross also testified that Pike
“was not brought up by” her mother because her mother was never at home, instead always
working or choosing to be “out partying.” Ross noted that, on one occasion, Ross and Hansen
were out at a bar when Hansen received a phone call that Pike, then a toddler, was experiencing
severe seizures that eventually required hospitalization. While Ross thought they should return
home to care for Pike, Hansen was unconcerned and wanted to remain at the bar. This was
merely indicative of the constant relationship between Hansen and Pike—whenever Hansen had
to act in either her own interest or Pike’s, Hansen always put herself first. Ross also discussed
the frequency with which Pike’s extended family all faced issues with substance abuse, as well
as numerous family members who were either physically or verbally abusive to their children
and grandchildren, including Pike.

       All in all, the jury heard a clear story: Pike’s childhood and upbringing were very
difficult and, in some ways, explained how she became a person capable of such a brutal murder.

       Pike now claims the jury should have received the more in-depth testimony on these
points that Dr. McCoy could have provided, but she fails to adequately explain how
Dr. McCoy’s testimony would “differ in a substantial way—in strength and subject matter—
from the evidence actually presented at sentencing.” 

. Although she
argues on appeal that the jury never heard that Pike’s parents’ inconsistency and lack of attention
to her well-being caused her “out of control” behavior, that point was made multiple times at the
penalty-phase hearing, with her mother even explicitly blaming herself for Pike’s behavior.
Thus, the evidence counsel presented to the jury encompassed the types of mitigating evidence
the Supreme Court has found valuable in other cases. See 

(finding
relevant mitigating evidence in verbal and physical parental abuse, inappropriate parental
discipline, and behavioral disorders); 

–35 (finding “powerful”
mitigating evidence in the defendant’s early childhood privation and abuse, an alcoholic and
absentee mother, and the physical abuse the defendant experienced). And, because the jury
 No. 16-5854                              Pike v. Gross                                 Page 11


heard largely the same narrative as Pike now presents, the Tennessee Court of Criminal Appeals’
conclusion that Pike failed to establish prejudice from Talman’s decision not to call Dr. McCoy
at the penalty-phase hearing, Pike, 

, at *51–52, was not an unreasonable
application of federal law under AEDPA. 28 U.S.C. § 2254(d).

                                               B.

       Pike next challenges Talman’s failure to investigate and discover other mitigating
evidence. The first evidence Pike claims Talman failed to discover was her diagnoses of bipolar
disorder, organic brain damage, and post-traumatic stress disorder (PTSD). She bases this
argument on her post-sentencing examination by Dr. Jonathan Pincus, who determined that she
actually suffered from organic brain damage, bipolar disorder and PTSD, rather than the
borderline personality disorder Dr. Engum diagnosed. Her argument fails for multiple reasons.

       First, “[a]bsent a showing that trial counsel reasonably believed that [the expert] was
somehow incompetent or that additional testing should have occurred, simply introducing the
contrary opinion of another mental health expert during habeas review is not sufficient to
demonstrate the ineffectiveness of trial counsel.” Hill v. Mitchell, 

, 944 (6th Cir.
2016) (alterations in original) (quoting McGuire v. Warden, Chillicothe Corr. Inst., 

, 758 (6th Cir. 2013)). Here, Dr. Engum testified that his expert opinion, after numerous
meetings with Pike and “fairly lengthy testing,” was that she suffered from “very severe
borderline personality disorder.” And he specifically testified that he tested Pike for brain
damage and his testing “unequivocally showed that she did not suffer any signs of brain
damage.”    Dr. McCoy also testified at a postconviction hearing that she concurred in Dr.
Engum’s medical assessment throughout her mitigation work on Pike’s case. So Talman had
two separate experts tell him that the correct diagnosis was borderline personality disorder. Even
assuming, for the sake of argument, that Dr. Pincus’s diagnoses of organic brain damage, bipolar
disorder, and PTSD are contrary to Dr. Engum’s diagnosis of borderline personality disorder,
nothing in the record shows that Talman should have reasonably believed that additional testing
was necessary. See 

                             Pike v. Gross                                  Page 12


       Furthermore, it is difficult to see how this alleged failure prejudiced Pike, when the jury
considered Dr. Engum’s testimony that Pike suffered from borderline personality disorder. Pike
does not specifically argue that the particular medical differences between borderline personality
disorder, bipolar disorder, PTSD, and organic brain damage would have influenced the jury in its
decision to sentence her to death. Instead, Pike argues that the presentation of evidence of
bipolar disorder and organic brain damage would have been relevant to prove to the jury that
Pike’s moral reasoning and impulse control were impaired—two deficits typically caused by
both organic brain damage and bipolar disorder. But the jury heard Dr. Engum testify that Pike
“did not act with deliberation, with premeditation, but instead, acted in a manner consistent with
her diagnosis, borderline personality disorder, which meant that she basically went out of
control. She basically lost any sense of what she was doing.” (Emphasis added). In other
words, the jury was already well aware of a medical expert’s opinion that her moral reasoning
and impulse control were not present during the murder of Colleen Slemmer. We doubt that the
substitution of bipolar disorder, PTSD, and organic brain damage for borderline personality
disorder would have affected the jury’s deliberations on this point. See 

;

.

       Pike also argues that her trial counsel was ineffective for failing to present various other
lay witnesses who could have testified about their relationships with Pike, what they thought of
her, and how she had described her tumultuous childhood in conversations. For example, she
argues that counsel should have presented the testimony of Marshall Muse, Pike’s teacher, who
would have testified that he saw “flashes [of] something special” in her. Or counsel should have
called an acquaintance named Onas Perry, who could have testified about her late-night talks
with Pike and how Pike had described a difficult childhood and home life. But, as noted above,
Pike has not persuaded us that this other testimony would have been significantly different in
strength or subject matter from the testimony of Pike’s mother, father, and aunt. 

. In sum, none of the evidence Pike now points to substantially differs from the mitigation
case that was presented to the jury.
 No. 16-5854                                      Pike v. Gross                                           Page 13


                                                         C.

        Finally, our conclusion is bolstered by the aggravating evidence before the jury. See
Bobby v. Van Hook, 

, 12–13 (2009) (per curiam) (noting that the strength of the
aggravating evidence against the defendant significantly diminished any effect additional
mitigating evidence might have had). The jury heard evidence that Pike and her accomplices
lured the victim into a lethal trap before torturing and taunting the victim until they killed her.
Pike left Slemmer’s body so badly beaten that the person who discovered it thought it was the
corpse of an animal before realizing it was a human body. 

. The jury
also heard Pike’s confession in which she admitted to slashing Slemmer’s throat multiple times,
throwing asphalt at her head, and even keeping a piece of her skull as a souvenir. 

allows a jury to impose a death sentence when a “murder [i]s especially heinous, atrocious or
cruel in that it involved torture or serious physical abuse beyond that necessary to produce
death,” see Tenn. Code Ann. § 39–13–204(i)(5). This crime fits that description.1

        It is true that “[t]he prejudice prong is satisfied if ‘there is a reasonable probability that at
least one juror would have struck a different balance.’” Dickerson v. Bagley, 

, 699
(6th Cir. 2006) (quoting 

), abrogated in part on other grounds by

–9. But a fairminded jurist could conclude that there is no such probability
here, where Pike’s desired evidence was mostly cumulative and insufficient to overcome the
heinous nature of her crime. Even were the jury to hear everything that Pike now wishes had
been presented, a fairminded jurist could conclude that the sheer weight and degree of
aggravation evidence before the jury outweighs the mitigation evidence raised on appeal. Cf.
Porter v. McCollum, 

, 41 (2009) (per curiam). Thus, the state court’s conclusion that
Pike could not establish Strickland prejudice, Pike, 

, at *51–52, was not an
unreasonable application of federal law. See 

–03. In short, because



        1The    jury also found that death was warranted because “[t]he murder was committed for the purpose of
avoiding, interfering with or preventing a lawful arrest or prosecution of the defendant or another.” See Tenn. Code
Ann. § 39–13–204(i)(6). Presumably, the jury came to this conclusion based upon Pike’s confession that she heard
“voices telling her that she had to do something to prevent Slemmer from telling on her and sending her to prison for
attempted murder.” 

. Pike did not refute this evidence, and this serves as another basis for
the death sentence.
 No. 16-5854                               Pike v. Gross                                Page 14


Pike fails to meet AEDPA’s stringent requirements, see 28 U.S.C. § 2254(d), she is ineligible for
habeas relief.

                                                IV.

       Because Petitioner cannot establish that the Tennessee Court of Criminal Appeals’
adjudication of her claims of ineffective assistance of counsel was an unreasonable application of
clearly established federal law, we affirm the judgment of the district court.
 No. 16-5854                                         Pike v. Gross                                           Page 15


                                                _________________

                                                 CONCURRENCE
                                                _________________

         JANE B. STRANCH, Circuit Judge, concurring. I join the opinion in this case but write
separately because it presents an issue with which our society must be concerned—whether
18-year-olds should be sentenced to death. Had she been 17 rather than 18 at the time of her
crime, like her codefendant Tadaryl Shipp, Christa Pike would not be eligible for the death
penalty.

         The difficulty of this case is not just age; the gravest concern arises from the combination
of Pike’s youth and the nature of her crime. Capital cases involve heinous and inexplicable
crimes, and Pike’s case presents no exception. But in sentencing Pike to death, we rule out the
possibility that her crime was a product of the immature mind of youth rather than fixed
depravity. And we presume that she is incapable of reform even though the stories of other
teenage killers, many of whom have been rehabilitated behind bars, reveal other possibilities. 1

         1A   few examples of teenagers initially sentenced to life in prison help explain the point.
Andrew      Hundley      was     15    years    old    when      he    killed   a    14-year-old    girl    “whose
body was found burned and badly beaten behind a grocery store.”               Grace Toohey, The Power of
Second Chances: How this 37-year-old, Once in Prison, Is Now an LSU Grad, The Advocate, May 10, 2019, https://
www.theadvocate.com/baton_rouge/news/crime_police/article_03c590ae-72a9-11e9-8d2b-4b78d19fcd5b html.
Now 37, Hundley helped found the Louisiana Parole Project and completed college coursework while in prison; he
finished his bachelor’s degree in sociology after being released on parole and plans to pursue a master’s degree in
criminology. 

was 16 when he stabbed another youth to death after an argument. Ted Roelofs, In Prison for Decades,
One      Juvenile    Lifer’s    Quest     for     Redemption,     Bridge    Magazine,     Aug.     26,     2016,
https://www.mlive.com/politics/2016/08/in_prison_for_decades_one_juve.html. Once in prison, Smith took
advantage of every rehabilitative program available to him, training Greyhounds so that they can be adopted by
families and winning the warden’s support for his release. 

was 16 years old, Kempis Songster stabbed another teenage runaway to death; after nearly three decades in
prison, he “is training to be a yoga instructor, leading workshops in cultural awareness, studying philosophy and
history . . . . He is doing everything, anything, really, to better himself, create a persona separate from his crime and
crushing sentence. He wants to make amends.” Amy S. Rosenberg, Teen Killers, Prison Lifers, Given a Ray of
Hope, Philadelphia Inquirer, Feb. 7, 2016, https://www.inquirer.com/news/inq/teen-killers-prison-lifers-given-ray-
hope-20160206 html.
Amaury Rosario was 17 when he, along with his codefendants, shot and killed four unarmed people during a
robbery gone wrong. United States v. Rosario, 99-cr-533, 12-cv-3432, 

, at *2 (E.D.N.Y. Aug. 9,
2018). After two decades in prison, guards as well as inmates attested to his character and positive influence;
moreover, mental-health experts working for both the defense and the prosecution at his resentencing agreed that
“he had been rehabilitated and . . . no longer poses a significant risk to the public.” 

 No. 16-5854                                Pike v. Gross                                  Page 16


The judgment that she merits the most severe punishment is in tension with Supreme Court
precedent focusing on the lesser blameworthiness and greater prospect for reform that is
characteristic of youth.

          In a series of cases starting with Roper v. Simmons, 

(2005), the Supreme
Court made clear that children are different from adults for purposes of the Eighth Amendment.
First, in Roper, the Court held that the Eighth Amendment’s “evolving standards of decency”
prohibit the imposition of death sentences on those who were under 18 at the time of their
crimes.      

571. Next, in Graham v. Florida, the Court concluded that juvenile
offenders who commit non-homicide offenses could not constitutionally be sentenced to life
without parole. 

, 74–75 (2010). Then, in Miller v. Alabama, the Court determined
that even juvenile homicide offenders could be sentenced to life without parole only after an
individualized sentencing hearing and a finding that their crime was not the product of
“unfortunate yet transient immaturity.” 

, 479–80 (2012). Finally, in Montgomery v.
Louisiana, the Court held that Miller was retroactively applicable because it announced a new
substantive rule—namely, “that sentencing a child to life without parole is excessive for all but
‘the rare juvenile offender whose crime reflects irreparable corruption.’” 

, 734
(2016) (quoting 

–80). Taken as a whole, these cases stand for the
principle that “[b]ecause juveniles have diminished culpability and greater prospects for
reform . . . , ‘they are less deserving of the most severe punishments.’” 

(quoting 

).

          This line of cases relied on three findings about the “significant gaps between juveniles
and adults” that make children “constitutionally different from adults for purposes of
sentencing.” 

have a ‘lack of maturity and an underdeveloped sense of
responsibility,’ leading to recklessness, impulsivity, and heedless risk-taking. Second, children
‘are more vulnerable . . . to negative influences and outside pressures’ . . . . And third, a child’s
character is not as ‘well formed’ as an adult’s . . . .” 

543 U.S. at 569–70).
These conclusions “rested not only on common sense . . . but on science and social science as
well.” Id.; see also 

n.5 (“The evidence presented to us in [Miller] indicates that the
 No. 16-5854                               Pike v. Gross                                   Page 17


science and social science supporting Roper’s and Graham’s conclusions have become even
stronger.”).

       Recent research in neuroscience and developmental psychology indicates that individuals
between the ages of 18 and 21 share many of these same characteristics. Since Roper was
decided, scientists have established that “biological and psychological development continues
into the early twenties.” Elizabeth S. Scott et al., Young Adulthood as a Transitional Legal
Category: Science, Social Change, and Justice Policy, 85 Fordham L. Rev. 641, 642 (2016).
Brain-imaging studies “have shown continued regional development of the prefrontal cortex,
implicated in judgment and self-control[,] beyond the teen years and into the twenties.”
Alexandra O. Cohen et al., When Does a Juvenile Become an Adult?, 88 Temp. L. Rev. 769, 783
& n.63 (2016) (collecting articles).      Researchers have found that in “negative emotional
situations,” such as conditions of threat, young adults between the ages of 18 and 21 perform
significantly worse than adults in their mid-20s—and more like those under 18. Alexandra O.
Cohen et al., When Is an Adolescent an Adult? Assessing Cognitive Control in Emotional and
Nonemotional Contexts, 27 Psychol. Sci. 549, 559–60 (2016). “It is also well established that
young adults, like teenagers, engage in risky behavior, such as . . . criminal activity, to a greater
extent than older adults.” Scott et 

. In short, empirical research has found that
“[a]lthough eighteen to twenty-one-year-olds are in some ways similar to individuals in their
midtwenties, in other ways, young adults are more like adolescents in their behavior,
psychological functioning, and brain development.” 

       Reflecting a long-held societal understanding of this point, we already recognize 21 as
the age of majority in a number of contexts. Individuals are required to be 21 to consume
alcohol or marijuana (where legal), purchase tobacco in many jurisdictions, or to rent a car.
Similarly, federal law prohibits licensed gun dealers from selling handguns and ammunition to
those under 21, see 18 U.S.C. § 922(b)(1), (c)(1), while immigration law allows U.S. citizens to
request immigrant visas for unmarried children under the age of 21, see 8 U.S.C. §§ 1101(b)(1),
1151(b)(2)(A)(i). In fact, 21 has traditionally marked the ascension to full adulthood: “[T]he
term ‘minor’ or ‘infant’—as those terms were historically understood—applied to persons under
the age of 21 . . . . The age of majority at common law was 21, and it was not until the 1970s
 No. 16-5854                               Pike v. Gross                                 Page 18


that States enacted legislation to lower the age of majority to 18.” NRA v. ATF, 

,
201 (5th Cir. 2012).

       For these reasons, I believe that society’s evolving standards of decency likely do not
permit the execution of individuals who were under 21 at the time of their offense. But, because
we review this case under the strictures of AEDPA, we may grant Pike relief only if the state
court’s adjudication of her case was either (1) contrary to or unreasonably applied Supreme
Court precedent, or (2) “resulted in a decision that was based on an unreasonable determination
of the facts.” 28 U.S.C. § 2254(d). And the Supreme Court has not extended Roper to 18-year-
olds. I therefore reluctantly concur because I agree that the state court’s decision denying Pike’s
postconviction petition did not unreasonably apply Strickland’s prejudice prong.