PATRICK E. HIGGINBOTHAM, Circuit Judge:

Petitioner-appellant Douglas Alan Feldman was convicted and sentenced to death in Texas for the 1998 murders of Robert Everett and Nicolas Velasquez. Feldman challenged his death sentence in habeas proceedings under 28 U.S.C. § 2254. The district court denied relief and Feldman now seeks a certificate of appealability. We deny Feldman's request.

I.

The facts of Feldman's crimes are essentially undisputed.1 Feldman was riding his motorcycle on the night of August 24, 1998 when Robert Everett, driving an eighteen-wheeler, suddenly passed Feldman and pulled into his lane, missing Feldman's left hand by inches. Enraged, Feldman took out his firearm and fired several shots into the back of Mr. Everett's trailer. Feldman then reloaded his weapon and pulled up alongside the cab of Mr. Everett's truck. He fired several shots directly at Mr. Everett, killing him.

After returning to the scene of the crime to verify that Mr. Everett was dead, Feldman headed home. Approximately 45 minutes after Feldman shot and killed Mr. Everett, and about eleven miles from the scene of the original shooting, Feldman passed an Exxon service station where Nicolas Velasquez, an Exxon tanker truck driver, was refilling the station's gas supply. Feldman drove into the station and shot Mr. Velasquez twice in the back, killing him. Feldman then returned home.

Over a week later, Feldman shot Antonio Vega while Mr. Vega was standing outside of a Jack-in-the-Box restaurant. Mr. Vega was seriously injured but survived. A bystander noted Feldman's license plate number and relayed the information to police. When the police apprehended Feldman, they recovered two firearms and hundreds of rounds of ammunition. Testing on one of the weapons and the shell casings found at the scene of the shootings of Messrs. Everett, Velasquez, and Vega confirmed that the weapon had been used at all three locations.

After his arrest but prior to trial, Feldman admitted committing the shootings to a police investigator, stating that they were the consequence of his traffic altercation with Mr. Everett. Feldman also testified to the shootings at his trial, noting that he had not forgiven Mr. Everett for his trespasses. Feldman explained that he had shot Mr. Velasquez because the man was standing beside an eighteen-wheeler, which caused Feldman to "explode[] again in anger."

Feldman was convicted of capital murder in a Texas trial court and sentenced to death on August 31, 1999. Feldman appealed to the Texas Court of Criminal Appeals ("the CCA"), which ultimately affirmed his conviction in a published opinion issued on February 20, 2002.2 Feldman did not seek review by petition of certiorari in the United States Supreme Court.

While his direct appeal was still pending, Feldman filed for state habeas relief under Article 11.071 of the Texas Code of Criminal Procedure. In accordance with Article 11.071, the convicting state trial court received briefs and supplemental affidavits from both Feldman and the state. However, the court denied Feldman's request for an additional evidentiary hearing to develop facts related to his habeas claims. The convicting trial court then issued findings of fact and conclusions of law on Feldman's habeas claims,3 which the CCA ultimately adopted in an unpublished opinion denying Feldman's request for habeas relief.4

Feldman filed his federal habeas petition on April 17, 2008. The district court denied both habeas relief and a certificate of appealability with respect to all of Feldman's claims.5 Feldman now seeks to appeal three of the four claims the district court rejected. First, Feldman argues that his death sentence violates his Sixth Amendment right to counsel, as his trial counsel rendered ineffective assistance by failing to present readily available evidence of Feldman's bipolar disorder.6 Next, Feldman claims that his trial denied him due process under the Fourteenth Amendment, as the trial judge refused to instruct the jury on the lesser-included offense of simple murder.7 Finally, Feldman claims that his trial denied him an impartial jury and due process in violation of the Sixth and Fourteenth Amendment, as the trial judge wrongfully excluded a qualified venire member merely because of her conscientious scruples about the death penalty.8

II.

Before a § 2254 petitioner can appeal, he must obtain a certificate of appealability ("COA").9 To obtain a COA, the petitioner must make "a substantial showing of the denial of a constitutional right."10 Where, as here, "a district court has rejected the constitutional claims on the merits, ... [t]he petitioner must demonstrate that reasonable jurists would find the district court's assessment of the constitutional claims debatable or wrong."11 In death penalty cases, "any doubts as to whether a COA should issue must be resolved in the petitioner's favor."12

The CCA adjudicated all of the claims Feldman seeks to appeal on the merits. Consequently, the district court's review of Feldman's claims was governed by 28 U.S.C. § 2254(d) and (e). Under § 2254(d), the district court could not grant habeas relief unless the CCA's adjudication (1) "resulted in a decision that 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) "resulted in a decision that was based on an unreasonable determination of the facts in light of the evidence presented in the State court proceeding."13 Moreover, under § 2254(e)(1), which supplements § 2254(d)(2) with an "arguably more deferential" standard of review for state court findings of fact,14 the district court was obliged to presume that the CCA's factual findings were correct unless Feldman furnished "clear and convincing evidence" otherwise.15

Hence, in determining whether a COA should issue in this case, the question is not whether reasonable jurists could debate the correctness of the CCA's rejection of Feldman's claims, but whether reasonable jurists could debate the district court's denial of habeas relief under the deferential standard of review mandated by § 2254(d) and (e).16

We examine Feldman's claims in turn and deny his request for a COA with respect to each claim.

III.

Feldman seeks to appeal the claim that his conviction requires reversal under Strickland v. Washington, arguing that his trial counsel's failure to present readily available mitigating evidence of Feldman's bipolar disorder amounted to deficient representation.

To prove that a conviction requires reversal under Strickland, a petitioner must show both that his trial counsel's performance was deficient and that the defense suffered prejudice as a consequence.17 To be cognizable under Strickland, trial counsel's error must be "so serious that counsel was not functioning as the "counsel" guaranteed the defendant by the Sixth Amendment."18 An error will meet this high standard if "counsel's representation fell below an objective standard of reasonableness."19 However, because of the risk that hindsight bias will cloud a court's review of counsel's trial strategy, "a court must indulge a strong presumption that counsel's conduct falls within the wide range of reasonable professional assistance; that is, the defendant must overcome the presumption that, under the circumstances, the challenged action might be considered sound trial strategy."20

Our evaluation of the appealability of Feldman's ineffective assistance claim requires a brief foray into the facts of the state proceedings below.21 In anticipation of the punishment phase of Feldman's trial, his defense counsel, James Oatman, retained a forensic psychiatrist and a psychologist to evaluate Feldman's mental condition.22 Feldman was uncooperative during the evaluation and the experts were unable to render a diagnosis.23 Concluding that the evaluation produced no mitigating evidence and actually disclosed facts harmful to Feldman, Mr. Oatman did not introduce evidence of the evaluation at trial.24

Nevertheless, Mr. Oatman's mitigation strategy rested on proving that Feldman had some form of mental deficiency that rendered him incapable of controlling his conduct.25 To make his case, Mr. Oatman relied on vague appeals to circumstantial evidence.26 Unsurprisingly, the prosecution rejoined that if Feldman truly suffered from a mental disorder, Mr. Oatman would have presented expert testimony.27 The prosecution also averred that if Feldman did suffer from any mental instability, it was due to his own voluntary drug use.28

In the subsequent habeas proceedings before the CCA, Feldman submitted evidence that Dr. Jeffrey Glass had diagnosed him with bipolar II disorder in 1997, about one year before the murders for which Feldman was convicted.29 Feldman also submitted evidence that his mother, Cecile Borshaw, had informed Mr. Oatman's investigator of Dr. Glass's 1997 diagnosis prior to trial, in accordance with Mr. Oatman's instructions to provide the investigator with all information relevant to the defense.30 Finally, Feldman introduced evidence of a post-conviction Bipolar I diagnosis obtained by his habeas counsel.31 In its answer, the prosecution submitted an affidavit from Mr. Oatman in which he generally explained his trial strategy but made no mention of the 1997 diagnosis.32

On the basis of this new evidence, Feldman claimed that Mr. Oatman's failure to procure and present expert testimony confirming Feldman's bipolar disorder constituted deficient representation under Strickland. Pointing to the post-conviction Bipolar I diagnosis obtained by habeas counsel and the pre-conviction Bipolar II diagnosis rendered by Dr. Glass, Feldman argued that Mr. Oatman clearly could have found a favorable expert had he been diligent.33

The CCA rejected Feldman's theory of deficiency, concluding that Feldman failed to overcome Strickland's "strong presumption" that trial counsel's representation was reasonable.34 The CCA reasoned that Mr. Oatman had diligently sought an experienced team of mitigation experts to evaluate Feldman's mental health, and that Mr. Oatman's representation was not deficient under Strickland merely because he did not "canvas the field to find a more favorable defense expert."35 Moreover, it reasoned that Mr. Oatman's decision not to obtain further evaluations could have been a reasonable strategic choice: even if he had been able to obtain a diagnosis akin to that obtained by Feldman's habeas counsel, the diagnosis would have been "double edged," demonstrating Feldman's future dangerousness.36

In the district court, Feldman argued that the CCA had erred for two reasons. First, he obliquely reasserted that reasonable trial counsel would have managed to procure and present a favorable mental health evaluation.37 In the alternative, he argued that Mr. Oatman still clearly erred by failing to introduce existing evidence of the 1997 diagnosis rendered by Dr. Glass.38

The district court rejected both of Feldman's theories of error under § 2254(d). First, it upheld as reasonable the CCA's conclusion that Strickland was not triggered by Mr. Oatman's failure to seek additional evaluations.39 Second, it concluded that Feldman's novel argument relating to the 1997 diagnosis ignored the "double edged" nature of the diagnosis as well as the fact that Mr. Oatman would have needed to find an expert willing to sponsor the diagnosis to present it to the jury.40

In his petition for a COA, Feldman claims that the district court erred in its analysis relating to Dr. Glass's 1997 diagnosis.41 Perhaps wisely, he does not resuscitate his claim that Mr. Oatman unreasonably failed to find an expert willing to render a new diagnosis.42 Consequently, we address only the former argument in this opinion.

At first blush, it appears difficult to reconcile Mr. Oatman's omission of the 1997 diagnosis with his mitigation strategy, particularly in light of the prosecution's response.43 However, Strickland requires a reviewing court "not simply to give [Mr. Oatman] the benefit of the doubt... but to affirmatively entertain the range of possible reasons [he] may have had for proceeding as [he] did."44 In this case, there are at least two plausible grounds for Mr. Oatman's omission.45 First, Mr. Oatman might have reasonably feared that introducing evidence of the 1997 diagnosis — which, as Feldman acknowledges, would have required the assistance of an expert sponsor46 — posed too great a risk of damaging cross examination by the prosecution.47 More importantly — and as Feldman conceded in habeas proceedings before the CCA — putting an expert on the stand to explain the diagnosis would have opened the door to the prosecution to bring in its own expert on rebuttal.48 As Mr. Oatman's own experts could not make a favorable diagnosis, he would have been foolhardy to ignore the risk that the prosecution could produce an adverse expert.49

In light of the sparse record evidence on the circumstances surrounding Mr. Oatman's omission of the 1997 diagnosis, the CCA was plainly justified in concluding that Feldman failed to overcome Strickland's "strong presumption" that Mr. Oatman's omission "might be considered sound trial strategy."50 Because jurists of reason could not debate the district court's denial of habeas relief under § 2254(d), we deny Feldman's application for a COA on his ineffective assistance claim.

IV.

Feldman also seeks to appeal his claim that the trial court violated his Fourteenth Amendment rights under Beck v. Alabama by refusing to instruct the jury on the lesser-included offense of simple murder.

Beck invalidated an Alabama statute that created a blanket ban prohibiting trial judges in capital murder trials from instructing a jury on the lesser-included offense of felony murder, even if there existed evidence of the lesser crime.51 The Supreme Court reasoned that the statute created a constitutionally impermissible risk that juries would return guilty verdicts not because they had found a defendant guilty of a capital crime, but because they believed a defendant to be guilty of some lesser-included crime and felt that he should be punished rather than set free.52

The Fifth Circuit has held that Beck requires a state trial court to give a lesser-included offense instruction "if the jury could rationally acquit on the capital crime and convict for the noncapital crime."53 Under Texas state law — which the Fifth Circuit has found consistent with Beck54 — the defendant is entitled to a requested lesser-included offense charge only if "the evidence of the lesser offense would be sufficient for a jury rationally to find that the defendant is guilty only of that offense, and not the greater offense."55

Under the Texas Penal Code, a defendant is guilty of capital murder if he commits more than one murder either "during the same criminal transaction ... or ... pursuant to the same scheme or course of conduct."56 The CCA has held that the latter category of capital murder includes "serial" murders.57 At trial, the prosecution charged Feldman with capital murder under both of the alternative routes available under the Penal Code, and the trial judge refused Feldman's request for a jury instruction on the lesser-included offense of simple murder.

In his direct appeal to the CCA, Feldman argued that Beck obligated the trial judge to instruct the jury on the lesser-include offense of simple murder. In rejecting Feldman's claim, the CCA conceded that a rational jury could have found that the murders did not occur "during the same criminal transaction," reasoning that the evidence showed a geographic and temporal gap between the two killings.58 However, it determined that a rational jury had to conclude that Feldman committed the murders "pursuant to the same scheme or course of conduct" — that is, that his murders were "serial" — noting that Feldman committed the murders "on the same evening with the same gun while out on a single car [sic] trip," and that Feldman himself had testified that he committed both killings in a fit of rage triggered by his initial traffic altercation with Mr. Everett.59 Though Feldman argued that his second murder was "motiveless," the CCA rejected this argument as having no basis in the record.60

In habeas proceedings before the district court, Feldman offered two theories as to why the CCA's adjudication of his Beck claim was unreasonable. First, Feldman made a conclusory assertion that the CCA erred in finding that no rational jury could acquit him of capital murder.61 Second, Feldman argued that because the CCA determined that a rational jury could have acquitted him on one of the two theories of capital murder charged by the prosecution, Beck required the CCA to hold that the trial court erred in not issuing an instruction for simple murder.62

In reviewing the CCA's decision, the district court began by observing that "Beck, strictly speaking, holds only that a state cannot impose a blanket ban on the giving of lesser-included offense instructions in a capital case."63 However, it found that "the Fifth Circuit has consistently applied Beck's holding when the state trial court refuses a lesser-included-offense instruction," and evaluated the CCA's decision under Fifth Circuit precedent.64

The district court rejected Feldman's first theory of error under § 2254(d), agreeing with the CCA that the record contained no evidence upon which a rational jury could have acquitted Feldman of capital murder.65 Proceeding to Feldman's second theory of error, that Beck mandates a simple murder instruction whenever a rational jury could acquit a defendant on one theory of capital murder, the district court held that Feldman's novel interpretation of Beck was clearly precluded by § 2254(d)(1).66

Feldman argues that reasonable jurists could dispute the district court's decision on both counts. We disagree. Even assuming that the district court was correct to evaluate Feldman's Beck claim under Fifth Circuit precedent,67 it was plainly justified in rejecting both of Feldman's theories under § 2254(d).68

As the CCA noted, Feldman's first theory of error — which amounts to little more than a conclusory assertion that a rational juror could have acquitted him of capital murder69 — is controverted by his testimony that he killed both Messrs. Everett and Velasquez in a fit of rage ignited by the initial traffic altercation with Mr. Everett. It is also controverted by Feldman's brief to this court, in which he concedes that he killed Mr. Velasquez because "[his] anger was unexpectedly rekindled by the sign of an Exxon truck driver refilling the fuel supply at a roadside gas station."70 Feldman's brief points to no evidence which would tend to show that the CCA's determination was incorrect, let alone unreasonable.71 Nor can we find any such evidence in the record.

Feldman's second theory of error relies on a tortured reading of Beck plainly precluded by § 2254(d)(1). Feldman claims that Beck mandates a lesser-included offense instruction whenever a rational juror could acquit the defendant on any one theory of capital murder. This reading of Beck ignores the case's underlying logic: where, as in this case, a defendant has been charged with capital murder under two separate theories, the Beck dilemma — that a jury might be coerced into returning an erroneous guilty verdict on a capital crime merely to avoid setting the defendant free — arises only if a rational jury could acquit the defendant on both theories.72 Feldman's incoherent reading of Beck cannot possibly be considered "clearly established Federal law" within the meaning of 2254(d)(1).73

V.

Finally, Feldman seeks to appeal the claim that his trial violated the Sixth and Fourteenth Amendment, arguing that the trial judge wrongfully excluded Ms. Diane Dreifke from the jury merely on the basis of her conscientious scruples against the death penalty.

In Witherspoon v. State of Illinois, the Supreme Court struck down a state statute that permitted the for-cause exclusion from a capital case of any juror who voiced "conscientious scruples against capital punishment."74 The Court reasoned that the statute impermissibly tilted juries in favor of capital punishment in violation of a defendant's Sixth and Fourteenth Amendment right to an impartial jury.75 However, in Wainwright v. Witt, the Supreme Court clarified that a juror could be excluded whenever his views would "prevent or substantially impair the performance of his duties as a juror in accordance with his instructions and his oath."76

Wainwright also emphasized that an exclusion order is not improper merely because the paper record fails to demonstrate a potential juror's bias with "unmistakable clarity."77 Because "many veniremen simply cannot be asked enough questions to reach the point where their bias has been made unmistakably clear," reviewing courts should generally defer to the determination of the trial judge, who sees and hears the juror.78 "[W]here ... there is lengthy questioning of a prospective juror and the trial court has supervised a diligent and thoughtful voir dire, the trial court has broad discretion."79

To assess the appealability of Feldman's claim, we briefly review the evidence in the record. At the beginning of the voir dire, Ms. Dreifke repeatedly stated that she supported the death penalty and could impose it in accordance with Texas law:

However, under subsequent questioning by the prosecution, Ms. Dreifke admitted that she had not given the death penalty much thought and began expressing doubts:

Moreover, once the prosecutor graphically described the execution process to Ms. Dreifke, she repeatedly stated that she did not think she could participate in a course of action that would result in the execution of another human being:

After the prosecution had finished questioning Ms. Dreifke, the trial judge gave the defense an opportunity to rehabilitate her. It declined.83

On direct appeal to the CCA, Feldman argued that the trial judge's exclusion of Ms. Dreifke from the jury violated Witherspoon and its progeny. The CCA rejected Feldman's claim, observing that "[b]ecause Dreifke vacillated on her ability to follow the law and ultimately told the court that she was not sure whether she could perform the duty entrusted her, the trial judge was within his discretion in determining that her views on capital punishment would have prevented or substantially impaired the performance of her duties as a juror in accordance with her instructions and her oath."84

In his brief to the district court, Feldman conceded that Ms. Dreifke found the prospect of imposing a death sentence emotionally difficult, but argued that her voir dire testimony — viewed as a whole — clearly indicates that she was willing and able to serve as a capital juror.85 After carefully examining the voir dire transcript, the district court upheld the CCA's determination as reasonable and denied habeas relief under § 2254(d).86

As the trial court's decision to exclude Ms. Dreifke was made after a thorough and fair voir dire process that included lengthy questioning by the prosecution and an opportunity for the defense to rehabilitate, the CCA would have been entitled to defer to that decision even if the printed record was ambiguous;87 as Feldman acknowledges in his brief, vacillating answers are a sufficient ground for exclusion.88 This, however, is a case where the printed record clearly supports a finding that Ms. Dreifke's views would have substantially impaired her ability to impose a capital sentence. Viewed chronologically, the record paints the picture of a juror who not only vacillated about her ability to impose a death sentence, but of one who — on gaining full information about the execution process — concluded that she was likely incapable of doing so.89

The CCA's rejection of Feldman's Witherspoon claim was thus plainly reasonable, and no jurist of reason could debate the district court's denial of habeas relief under § 2254(d).90

VI.

The motion for a certificate of appealability is DENIED.