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6 

SHOOP v. TWYFORD 

Opinion of the Court 

and  federalism,”  Williams  v.  Taylor,  529  U. S.  420,  436 
(2000)  (Michael  Williams).  It  furthered  those  goals  “in 
large measure [by] revising the standards used for evaluat-
ing the merits of a habeas application.”  Garceau, 538 U. S., 
at  206.  Pertinent  here,  §2254(d)  provides  that  if  a  claim
was adjudicated on the merits in state court, a federal court 
cannot grant relief unless the state court (1) contradicted or
unreasonably applied this Court’s precedents, or (2) handed
down a decision “based on an unreasonable determination 
of the facts in light of the evidence presented in the State
court proceeding.”  The question under AEDPA is thus not 
whether a federal court believes the state court’s determi-
nation was incorrect, but whether that determination was 
unreasonable—“a  substantially  higher  threshold”  for  a
prisoner to meet.  Schriro v. Landrigan, 550 U. S. 465, 473 
(2007);  see  also  Harrington  v.  Richter,  562  U. S.  86,  102– 
103 (2011).

AEDPA also restricts the ability of a federal habeas court 
to  develop  and  consider  new  evidence.    Review  of  factual 
determinations  under  §2254(d)(2)  is  expressly  limited  to
“the evidence presented in the State court proceeding.”  And 
in Cullen v. Pinholster, 563 U. S. 170 (2011), we explained 
that review of legal claims under §2254(d)(1) is also “limited 
to the record that was before the state court.”  Id., at 181. 
This ensures that the “state trial on the merits” is the “main 
event, so to speak, rather than a tryout on the road for what 
will  later  be  the  determinative  federal  habeas  hearing.” 
Wainwright v. Sykes, 433 U. S. 72, 90 (1977) (internal quo-
tation marks omitted).

If a prisoner “failed to develop the factual basis of a claim 
in State court proceedings,” a federal court may admit new 
evidence,  but  only  in  two  quite  limited  situations. 
§2254(e)(2).  Either the claim must rely on a “new” and “pre-
viously unavailable” “rule of constitutional law” made ret-
roactively applicable by this Court, or it must rely on “a fac-
tual  predicate  that  could  not  have  been  previously