(Slip Opinion)              OCTOBER TERM, 2008                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

                       BOBBY, WARDEN v. BIES

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                  THE SIXTH CIRCUIT

       No. 08–598.      Argued April 27, 2009—Decided June 1, 2009
In Atkins v. Virginia, 536 U. S. 304, this Court held that the Eighth
  Amendment bars execution of mentally retarded offenders. Prior to
  Atkins, mental retardation merited consideration as a mitigating fac
  tor, but did not bar imposition of the death penalty. See Penry v. Ly
  naugh, 492 U. S. 302. Nearly a decade before Atkins, respondent
  Bies was tried and convicted in Ohio of the aggravated murder, kid
  naping, and attempted rape of a ten-year-old boy. Instructed at the
  sentencing stage to weigh mitigating circumstances (including evi
  dence of Bies’ mild to borderline mental retardation) against aggra
  vating factors (including the crime’s brutality), the jury recommended
  a death sentence, which the trial court imposed. Ohio’s Court of Ap
  peals and Supreme Court affirmed the conviction and sentence, each
  concluding that Bies’ mental retardation was entitled to “some
  weight” as a mitigating factor, but that the aggravating circum
  stances outweighed the mitigating circumstances. Bies then filed an
  unsuccessful petition for state postconviction relief, contending for
  the first time that the Eighth Amendment prohibits execution of a
  mentally retarded defendant. Soon after Bies sought federal habeas
  relief, this Court decided Atkins. The opinion left to the States the
  task of developing appropriate ways to determine when a person
  claiming mental retardation would fall within Atkins’ compass. Ohio
  heeded Atkins’ call in State v. Lott. The District Court then stayed
  Bies’ federal habeas proceedings so that he could present an Atkins
  claim to the state postconviction court. Observing that Bies’ mental
  retardation had not previously been established under the Atkins-
  Lott framework, the state court denied Bies’ motion for summary
  judgment and ordered a full hearing on the Atkins claim. Rather
  than proceeding with that hearing, Bies returned to federal court, ar
2                             BOBBY v. BIES

                                  Syllabus

    guing that the Double Jeopardy Clause barred the State from reliti
    gating the mental retardation issue. The District Court granted the
    habeas petition, and the Sixth Circuit affirmed. Relying on Ashe v.
    Swenson, 397 U. S. 436, the Court of Appeals determined that all re
    quirements for the issue preclusion component of the Double Jeop
    ardy Clause were met in Bies’ case. It concluded, inter alia, that the
    Ohio Supreme Court, on direct appeal, had decided the mental retar
    dation issue under the same standard that court later adopted in
    Lott, and that the state court’s recognition of Bies’ mental state had
    been necessary to the death penalty judgment. When the Sixth Cir
    cuit denied the State’s petition for rehearing en banc, a concurring
    judge offered an alternative basis for decision. He opined that, under
    Sattazahn v. Pennsylvania, 537 U. S. 101, jeopardy attaches once a
    capital defendant is “acquitted” based on findings establishing an en
    titlement to a life sentence; reasoning that the Ohio courts’ mental
    retardation findings entitled Bies to a life sentence, he concluded that
    the Double Jeopardy Clause barred any renewed inquiry into Bies’
    mental state.
Held: The Double Jeopardy Clause does not bar the Ohio courts from
 conducting a full hearing on Bies’ mental capacity. Pp. 7–11.
    (a) The alternative basis for decision offered by the concurring
 opinion at the Sixth Circuit’s rehearing stage is rejected. The State
 did not “twice put [Bies] in jeopardy,” U. S. Const., Amdt. 5, in the
 core constitutional sense. Sattazahn offers Bies no aid, for there was
 no acquittal here. Bies’ jury voted to impose the death penalty. At
 issue is his attempt to vacate that sentence, not an effort by the State
 to retry him or to increase his punishment. Nor did the state courts’
 mental retardation determinations entitle Bies to a life sentence. At
 the time of his sentencing and direct appeal, Penry, not Atkins, was
 the guiding decision, and the dispositive issue was whether the miti
 gating factors were outweighed by the aggravating circumstances be
 yond a reasonable doubt. Pp. 7–8.
    (b) The issue preclusion doctrine, on which the Sixth Circuit panel
 primarily relied, does not bar a full airing of the issue whether Bies
 qualifies as mentally retarded under Atkins and Lott. The doctrine
 bars relitigation of issues actually determined and necessary to the
 ultimate outcome of a prior proceeding. Initially, it is not clear that
 the issue of Bies’ mental retardation was actually determined under
 the Lott test at trial or on direct appeal. Nor did the State concede
 that Bies would succeed under Atkins and Lott, which had not then
 been decided. More fundamental, it is clear that the state courts’
 statements regarding Bies’ mental capacity were not necessary to the
 judgments affirming his death sentence. Instead, those determina
 tions cut against the ultimate outcome. In holding otherwise, the
                     Cite as: 556 U. S. ____ (2009)                    3

                                Syllabus

  Sixth Circuit conflated a determination necessary to the bottom-line
  judgment with a subsidiary finding that, standing alone, is not out
  come determinative. The Sixth Circuit also erred in relying on Ashe’s
  statement: “[W]hen an issue of ultimate fact has once been deter
  mined by a valid and final judgment, that issue cannot again be liti
  gated between the same parties in any future lawsuit.” 397 U. S., at
  443. Bies’ case does not involve the kind of “ultimate fact” addressed
  in Ashe. There, the State was precluded from trying Ashe for robbing
  a poker player because he had already been acquitted of robbing a
  different player in the same poker game, and the acquittal was based
  on a determination that Ashe was not a participant in the poker
  game robbery. Bies, in contrast, was not acquitted, and determina
  tions of his mental capacity were not necessary to the ultimate impo
  sition of the death penalty. Moreover, even if the core issue preclu
  sion requirements had been met, an exception to the doctrine’s
  application would be warranted due to the intervening Atkins deci
  sion. Mental retardation as a mitigator and mental retardation un
  der Atkins and Lott are discrete legal issues. One difference is that
  mental retardation, urged as a mitigating factor, may instead “en
  hance the likelihood that [a jury will find] the aggravating factor of
  future dangerousness.” Atkins 536 U. S., at 521. This reality ex
  plains why prosecutors, pre-Atkins, had little incentive to contest re
  tardation evidence. Because the change in law substantially altered
  the State’s incentive to contest Bies’ mental capacity, applying pre
  clusion would not advance the equitable administration of the law.
  The federal courts’ intervention in this case derailed the state-court
  proceeding. Recourse first to Ohio’s courts is what this Court envi
  sioned in remitting to the States responsibility for implementing At
  kins. The State acknowledges that Bies is entitled to such recourse,
  but rightly seeks a full and fair opportunity to contest his plea under
  the Atkins and Lott precedents. Pp. 8–11.
519 F. 3d 324, reversed and remanded.

  GINSBURG, J., delivered the opinion for a unanimous Court.
                       Cite as: 556 U. S. ____ (2009)                              1

                            Opinion of the Court

    NOTICE: This opinion is subject to formal revision before publication in the
    preliminary print of the United States Reports. Readers are requested to
    notify the Reporter of Decisions, Supreme Court of the United States, Wash
    ington, D. C. 20543, of any typographical or other formal errors, in order
    that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                  _________________

                                  No. 08–598
                                  _________________


       DAVID BOBBY, WARDEN, PETITIONER v.

                 MICHAEL BIES 

 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

            APPEALS FOR THE SIXTH CIRCUIT

                                [June 1, 2009]


   JUSTICE GINSBURG delivered the opinion of the Court.
   In Atkins v. Virginia, 536 U. S. 304 (2002), this Court
held that the Eighth Amendment’s prohibition of “cruel
and unusual punishments” bars execution of mentally
retarded offenders. Prior to Atkins, the Court had deter
mined that mental retardation merited consideration as a
mitigating factor, but did not bar imposition of the death
penalty. See Penry v. Lynaugh, 492 U. S. 302 (1989).
   In 1992, nearly a decade before the Court’s decision in
Atkins, respondent Michael Bies was tried and convicted
in Ohio of the aggravated murder, kidnaping, and at
tempted rape of a ten-year-old boy. Instructed at the
sentencing stage to weigh mitigating circumstances (in
cluding evidence of Bies’ mild to borderline mental retar
dation) against aggravating factors (including the brutal
ity of the crime), the jury recommended a sentence of
death, which the trial court imposed. Ohio’s appellate
courts affirmed the conviction and sentence. The Ohio
Supreme Court, in its 1996 opinion on direct review, ob
served that Bies’ “mild to borderline mental retardation
merit[ed] some weight in mitigation,” but concluded that
2                            BOBBY v. BIES

                           Opinion of the Court

“the aggravating circumstances outweigh[ed] the mitigat
ing factors beyond a reasonable doubt.” State v. Bies, 74
Ohio St. 3d 320, 328, 658 N. E. 2d 754, 761–762.
   After this Court decided Atkins, the Ohio trial court
ordered a full hearing on the question of Bies’ mental
capacity. The federal courts intervened, however, grant
ing habeas relief to Bies, and ordering the vacation of his
death sentence. Affirming the District Court’s judgment,
the Sixth Circuit reasoned that the Ohio Supreme Court,
in 1996, had definitively determined, as a matter of fact,
Bies’ mental retardation. That finding, the Court of Ap
peals concluded, established Bies’ “legal entitlement to a
life sentence.” Bies v. Bagley, 519 F. 3d 324, 334, n. 6
(CA6 2008). Therefore, the Sixth Circuit ruled, the Double
Jeopardy Clause of the Federal Constitution barred any
renewed inquiry into the matter of Bies’ mental state.
   We reverse the judgment of the Court of Appeals. The
Sixth Circuit, in common with the District Court, funda
mentally misperceived the application of the Double Jeop
ardy Clause and its issue preclusion (collateral estoppel)
component.1 First, Bies was not “twice put in jeopardy.”
He was sentenced to death, and Ohio sought no further
prosecution or punishment. Instead of “serial prosecutions
by the government[,] this case involves serial efforts by the
defendant to vacate his capital sentence.” Bies v. Bagley,
535 F. 3d 520, 531–532 (CA6 2008) (Sutton, J., dissenting
from denial of rehearing en banc) (internal quotation
marks omitted). Further, mental retardation for purposes
of Atkins, and mental retardation as one mitigator to be
weighed against aggravators, are discrete issues. Most
grave among the Sixth Circuit’s misunderstandings, issue

——————
    1 “[R]eplac[ing]a more confusing lexicon,” the term “issue preclusion,”
in current usage, “encompasses the doctrines [earlier called] ‘collateral
estoppel’ and ‘direct estoppel.’ ” Taylor v. Sturgell, 553 U. S. ___, ___, n.
5 (2008) (slip op., at 9, n. 5).
                 Cite as: 556 U. S. ____ (2009)           3

                     Opinion of the Court

preclusion is a plea available to prevailing parties. The
doctrine bars relitigation of determinations necessary to
the ultimate outcome of a prior proceeding. The Ohio
courts’ recognition of Bies’ mental state as a mitigating
factor was hardly essential to the death sentence he re
ceived. On the contrary, the retardation evidence cut
against the final judgment. Issue preclusion, in short,
does not transform final judgment losers, in civil or crimi
nal proceedings, into partially prevailing parties.
                              I
  For his part in brutally causing the death of a ten-year
old boy, Bies was convicted by an Ohio jury of attempted
rape, kidnaping, and aggravated murder with three death
penalty specifications. App. 85; Ohio Rev. Code Ann.
§2929.04(A)(3), (7) (Lexis 2006).
  At sentencing, Bies presented testimony from clinical
psychiatrist Donna E. Winter, who had evaluated him at
the court’s order during the guilt phase and again before
the mitigation hearing. App. 191, 202. Bies did not
qualify for a plea of not guilty by reason of insanity, Dr.
Winter concluded, because he knew the difference between
right and wrong at the time of the offense. Id., at 36, 51,
198–200. Bies’ IQ, she further reported, fell in the 65–75
range, id., at 211–212, indicating that he is “mildly
mentally retarded to borderline mentally retarded,” id., at
20–21, 32, 199–200, 213. Dr. Winter also observed: “[Bies]
goes about the community, unassisted [and] carries out
the activities of daily life fairly independently.” Id., at
199. The State responded to Bies’ mitigating evidence by
emphasizing the brutality of the murder and the risk of
Bies’ future dangerousness. Instructed to weigh the
mitigating circumstances against aggravating factors, the
jury recommended a death sentence, which the trial court
imposed. Id., at 88–89.
  The Ohio Court of Appeals and Supreme Court each
4                      BOBBY v. BIES

                     Opinion of the Court

independently reviewed the evidence and affirmed. Id., at
84–108; Bies, 74 Ohio St. 3d 320, 658 N. E. 2d 754.
Neither court devoted detailed attention to the issue of
retardation. Both concluded that Bies’ mild to borderline
mental retardation merited “some weight” in mitigation,
as did his youth and lack of a criminal record. App. 105–
106; 74 Ohio St. 3d, at 328, 658 N. E. 2d, at 762. The
aggravating      circumstances,      each    court    found,
overwhelmed the mitigating circumstances beyond a
reasonable doubt. App. 106; 74 Ohio St. 3d, at 328, 658
N. E. 2d, at 762. We denied Bies’ petition for a writ of
certiorari. Bies v. Ohio, 517 U. S. 1238 (1996).
  Bies then filed a petition for state postconviction relief,
contending for the first time that the Eighth Amendment
to the Federal Constitution prohibits execution of a men
tally retarded defendant. The trial court agreed that Bies
was “mildly mentally retarded,” but concluded that, under
then-governing Ohio precedent, “a mildly mentally re
tarded defendant may be [p]unished by execution.” App.
153. The Ohio Court of Appeals affirmed the judgment,
id., at 175–176, and the Ohio Supreme Court dismissed
Bies’ appeal without an opinion, State v. Bies, 87 Ohio St.
3d 1440, 719 N. E. 2d 4 (1999) (Table).
  Bies next filed a federal habeas petition in the United
States District Court for the Southern District of Ohio.
Soon after that filing, this Court held, in Atkins v. Vir
ginia, 536 U. S., at 321, that the Eighth Amendment
prohibits execution of mentally retarded offenders. Our
opinion did not provide definitive procedural or
substantive guides for determining when a person who
claims mental retardation “will be so impaired as to fall
[within Atkins’ compass].” We “ le[ft] to the States the
task of developing appropriate ways to enforce the
constitutional restriction.” Id., at 317 (internal quotation
marks omitted).
  Ohio heeded Atkins’ call six months later in State v.
                 Cite as: 556 U. S. ____ (2009)            5

                     Opinion of the Court

Lott, 97 Ohio St. 3d 303, 2002–Ohio–6625, 779 N. E. 2d
1011 (per curiam). At an Atkins hearing, the Ohio
Supreme Court held, a defendant must prove: “(1)
significantly subaverage intellectual functioning, (2)
significant limitations in two or more adaptive skills, such
as communication, self-care, and self-direction, and (3)
onset before the age of 18.” 97 Ohio St. 3d, at 305, 779
N. E. 2d, at 1014. “IQ tests,” the court stated, “are one of
the many factors that need to be considered, [but] they
alone are not sufficient to make a final determination [of
retardation].”     Ibid.   The court also announced “a
rebuttable presumption that a defendant is not mentally
retarded if his or her IQ is above 70.” Ibid.
  The District Court stayed its proceedings on Bies’
federal habeas petition while Bies presented an Atkins
claim to the state postconviction court. App. to Pet. for
Cert. 83a. Bies there moved for summary judgment,
arguing that the record established his mental
retardation, and that the State was “precluded and
estopped” from disputing it. Id., at 104a. The state court
recognized that Atkins and Lott had materially changed
the significance of a mental retardation finding. The court
observed that mental retardation had not previously been
established under the Atkins-Lott framework; given those
precedent-setting decisions, the court concluded, “there is
a serious issue as to Mr. Bies’ mental status.” App. to Pet.
for Cert. 104a. Accordingly, the court denied summary
judgment and ordered a full hearing on the Atkins claim.
  Rather than proceeding with the hearing directed by the
state court, Bies returned to the Federal District Court.
He argued that the Fifth Amendment’s Double Jeopardy
Clause, made applicable to the States by the Fourteenth
Amendment, barred the State from relitigating the issue
of his mental condition. App. to Pet. for Cert. 81a. The
District Court granted the habeas petition and ordered
vacation of Bies’ death sentence. Id., at 68a.
6                      BOBBY v. BIES

                     Opinion of the Court

   The Court of Appeals affirmed. 519 F. 3d 324, 342. It
concluded that Bies’ case was “controlled by” Ashe v.
Swenson, 397 U. S. 436 (1970), which held that the doc
trine of issue preclusion “is embodied in the Fifth Amend
ment guarantee against double jeopardy.” 519 F. 3d, at
332 (quoting 397 U. S., at 445). The Court of Appeals
found all requirements for issue preclusion met in Bies’
case. It concluded, inter alia, that the Ohio Supreme
Court, in resolving Bies’ direct appeal, had decided the
issue of Bies’ mental retardation under the same standard
later adopted in Lott. 519 F. 3d, at 336. Further, the
Court of Appeals held, the state court’s recognition that
Bies qualified as mentally retarded had been necessary to
the judgment imposing the death sentence. “[D]etermining
which mitigating factors are actually present,” the court
reasoned, “is a necessary first step to determining whether
those factors outweigh the aggravating circumstances.”
Id., at 337.
   The Court of Appeals denied the State’s petition for
rehearing en banc. 535 F. 3d 520. Judge Clay, concur
ring, opined that Sattazahn v. Pennsylvania, 537 U. S. 101
(2003), provided an additional, independent basis for
affirmance. 535 F. 3d, at 523–524. Under that decision,
he noted, jeopardy attaches, and relitigation is precluded,
once a judge or jury has “acquitted” a capital defendant
“by entering findings sufficient to establish legal entitle
ment to [a] life sentence.” Id., at 522 (quoting Sattazahn,
537 U. S., at 108–109). In Bies’ case, Judge Clay con
cluded, the Ohio courts’ determination of mental retarda
tion “entitle[d]” Bies to a life sentence, and thus the Dou
ble Jeopardy Clause barred the State from disputing the
issue of Bies’ mental retardation. 535 F. 3d, at 523–524.
   Judge Sutton dissented from the denial of rehearing en
banc. Sattazahn was inapposite, he maintained, because
Bies was never “twice put in jeopardy.” 535 F. 3d, at 531
(internal quotation marks omitted). Nor, in Judge Sut
                 Cite as: 556 U. S. ____ (2009)            7

                     Opinion of the Court

ton’s view, did Ashe support the panel’s decision, for issue
preclusion did not come into play in Bies’ case. 535 F. 3d,
at 532.
  We granted certiorari, 555 U. S. ___ (2009), and now
reverse.
                              II 

                              A

    The alternative basis for decision offered at the rehear
ing stage in the Court of Appeals can be rejected without
extensive explanation. The State did not “twice put [Bies]
in jeopardy,” U. S. Const., Amdt. 5, in the core constitu
tional sense. “[T]he touchstone for double-jeopardy protec
tion in capital-sentencing proceedings is whether there
has been an ‘acquittal.’ ” Sattazahn, 537 U. S., at 109.
Sattazahn offers Bies no aid. In that case, the defendant’s
first capital jury had deadlocked at the penalty phase, and
the court, as required by state law, entered a life sentence.
Id., at 104–105. This Court held the Double Jeopardy
Clause did not bar the State’s request for the death pen
alty at the defendant’s retrial, noting that “neither the
judge nor the jury had acquitted the defendant in his first
. . . proceeding by entering findings sufficient to establish
legal entitlement to the life sentence.” Id., at 108–109
(internal quotation marks omitted).
    Here, as in Sattazahn, there was no acquittal. Bies’ jury
voted to impose the death penalty. At issue now is Bies’
“second run at vacating his death sentence,” 535 F. 3d, at
531 (Sutton, J., dissenting from denial of rehearing en
banc), not an effort by the State to retry him or to increase
his punishment.
    Nor did any state-court determination of Bies’ mental
retardation “entitl[e]” him to a life sentence. Cf. id., at
523 (Clay, J., concurring in denial of rehearing en banc).
At the time Bies was sentenced and on direct appeal,
Penry, not Atkins, was this Court’s guiding decision.
8                       BOBBY v. BIES

                      Opinion of the Court

Under Penry, no single mitigator or aggravator was de
terminative of the judgment. Instead, the dispositive
issue, correctly comprehended by the Ohio courts, was
whether “the aggravating circumstances outweigh[ed] the
mitigating factors beyond a reasonable doubt.” Bies, 74
Ohio St. 3d, at 328, 658 N. E. 2d, at 762.
                               B
   The Court of Appeals panel relied primarily on the
doctrine of issue preclusion, recognized in Ashe to be “em
bodied in” the Double Jeopardy Clause. 397 U. S., at 445.
Preclusion doctrine, however, does not bar a full airing of
the issue whether Bies qualifies as mentally retarded
under Atkins and Lott.
   Issue preclusion bars successive litigation of “an issue of
fact or law” that “is actually litigated and determined by a
valid and final judgment, and . . . is essential to the judg
ment.” Restatement (Second) of Judgments §27 (1980)
(hereinafter Restatement). If a judgment does not depend
on a given determination, relitigation of that determina
tion is not precluded. Id., §27, Comment h. In addition,
even where the core requirements of issue preclusion are
met, an exception to the general rule may apply when a
“change in [the] applicable legal context” intervenes. Id.,
§28, Comment c.
   As an initial matter, it is not clear from the spare
statements of the Ohio appellate courts that the issue of
Bies’ mental retardation under the Lott test was actually
determined at trial or during Bies’ direct appeal. No court
found, for example, that Bies suffered “significant
limitations in two or more adaptive skills.” Lott, 97 Ohio
St. 3d, at 305, 779 N. E. 2d, at 1014. Nor did the State
concede that Bies would succeed under Atkins and Lott,
which had not then been decided.
   More fundamental, it is clear that the courts’ statements
regarding Bies’ mental capacity were not necessary to the
                 Cite as: 556 U. S. ____ (2009)           9

                     Opinion of the Court

judgments affirming his death sentence. A determination
ranks as necessary or essential only when the final out
come hinges on it. See 18 C. Wright, A. Miller, & E.
Cooper, Federal Practice and Procedure §4421, p. 543 (2d
ed. 2002). “Far from being necessary to the judgment, the
Ohio courts’ mental-retardation findings cut against it—
making them quintessentially the kinds of rulings not
eligible for issue-preclusion treatment.” 535 F. 3d, at 533
(Sutton, J., dissenting from denial of rehearing en banc).
   In finding the state court’s determination “necessary to
[the] judgment,” 519 F. 3d, at 342, the Court of Appeals
panel reasoned that the Ohio courts determined Bies’
mental capacity pursuant to their “mandatory duty” to
weigh the aggravating and mitigating circumstances. Id.,
at 338. “[W]eighing [aggravators against mitigators],” the
panel explained, “could not have occurred unless the court
first determined what to place on either side of the scale.”
Ibid. This reasoning conflates a determination necessary
to the bottom-line judgment with a subsidiary finding
that, standing alone, is not outcome determinative. Issue
preclusion cannot transform Bies’ loss at the sentencing
phase into a partial victory.
   For the same reason, the Court of Appeals erred in its
repeated reliance on the following passage in Ashe: “When
an issue of ultimate fact has once been determined by a
valid and final judgment, that issue cannot again be
litigated between the same parties in any future lawsuit.”
519 F. 3d, at 331–333 (quoting 397 U. S., at 443). Bies’
case does not involve an “ultimate fact” of the kind our
decision in Ashe addressed. There, the State sought to try
Ashe for robbing a poker player even though a jury had
already acquitted him of robbing a different player in the
same poker game. The State’s second attempt was pre
cluded, we held, because the first jury had based its ver
dict of acquittal upon a determination that Ashe was not
one of the participants in the poker game robbery. Id., at
10                          BOBBY v. BIES

                          Opinion of the Court

445. Bies, in contrast, was not acquitted—and, as already
observed, determinations of his mental capacity were not
necessary to the ultimate imposition of the death penalty.2
   Moreover, even if the core requirements for issue pre
clusion had been met, an exception to the doctrine’s appli
cation would be warranted due to this Court’s intervening
decision in Atkins. Mental retardation as a mitigator and
mental retardation under Atkins and Lott are discrete
legal issues. The Atkins decision itself highlights one
difference: “[R]eliance on mental retardation as a mitigat
ing factor can be a two-edged sword that may enhance the
likelihood that the aggravating factor of future danger
ousness will be found by the jury.” 536 U. S., at 321. This
reality explains why prosecutors, pre-Atkins, had little
incentive vigorously to contest evidence of retardation.
See App. 65 (excerpt from prosecutor’s closing argument
describing as Bies’ “[c]hief characteristic” his “sensitivity
to any kind of frustration and his rapid tendency to get
enraged”); id., at 39–54 (cross-examination of Bies’ expert
witness designed to emphasize Bies’ dangerousness to
others). Because the change in law substantially altered
the State’s incentive to contest Bies’ mental capacity,
applying preclusion would not advance the equitable
administration of the law. See Restatement §28, Com
ment c.
   The federal courts’ intervention in this case derailed a
state trial court proceeding “designed to determine
whether Bies ha[s] a successful Atkins claim.” 535 F. 3d,
——————
  2 This case, we note, is governed by the Antiterrorism and Effective
Death Penalty Act of 1996. Bies plainly fails to qualify for relief under
that Act: The Ohio courts’ decisions were not “contrary to, or . . . an
unreasonable application of, clearly established Federal law,” 28
U. S. C. §2254(d)(1), and were not “based on an unreasonable determi
nation of the facts in light of the evidence presented in the State court
proceeding,” §2254(d)(2). See also 535 F. 3d, at 534 (CA6 2008) (Sutton,
J., dissenting from denial of rehearing en banc).
                 Cite as: 556 U. S. ____ (2009)           11

                     Opinion of the Court

at 534 (Sutton, J., dissenting from denial of rehearing en
banc). Recourse first to Ohio’s courts is just what this
Court envisioned in remitting to the States responsibility
for implementing the Atkins decision. The State acknowl
edges that Bies is entitled to such recourse, but it rightly
seeks a full and fair opportunity to contest his plea under
the postsentencing precedents set in Atkins and Lott.
                       *     *    *
  For the reasons stated, the judgment of the Court of
Appeals is reversed, and the case is remanded for further
proceedings consistent with this opinion.
                                          It is so ordered.
