Reasonable people of good faith disagree on the morality and efficacy of capital punishment, and for many who oppose it, no method of execution would ever be acceptable. But as Justice Frankfurter stressed in Resweber, “[o]ne must be on guard against finding in personal disapproval a reflection of more or less prevailing condemnation.” 329 U. S., at 471 (concurring opinion). This Court has ruled that capital punishment is not prohibited under our Constitution, and that the States may enact laws specifying that sanction. “[T]he power of a State to pass laws means little if the State cannot enforce them.” McCleskey v. Zant, 499 U. S. 467, 491 (1991). State efforts to implement capital punishment must certainly comply with the Eighth Amendment, but what that Amendment prohibits is wanton exposure to “objectively intolerable risk,” Farmer, 511 U. S., at 846, and n. 9, not simply the possibility of pain.

Kentucky has adopted a method of execution believed to be the most humane available, one it shares with 35 other States. Petitioners agree that, if administered as intended, that procedure will result in a painless death. The risks of maladministration they have suggested—such as improper mixing of chemicals and improper setting of IVs by trained and experienced personnel—cannot remotely be characterized as “objectively intolerable.” Kentucky’s decision to adhere to its protocol despite these asserted risks, while adopting safeguards to protect against them, cannot be viewed as probative of the wanton infliction of pain under the Eighth Amendment. Finally, the alternative that petitioners belatedly propose has problems of its own, and has never been tried by a single State.

Throughout our history, whenever a method of execution has been challenged in this Court as cruel and unusual, the Court has rejected the challenge. Our society has nonetheless steadily moved to more humane methods of carrying out capital punishment. The firing squad, hanging, the electric chair, and the gas chamber have each in turn given way to more humane methods, culminating in today’s consensus on lethal injection. Gomez v. United States Dist. Court for Northern Dist. of Cal., 503 U. S. 653, 657 (1992) (STEVENS, J., dissenting); App. 755. The broad framework of the Eighth Amendment has accommodated this progress toward more humane methods of execution, and our approval of a particular method in the past has not precluded legislatures from taking the steps they deem appropriate, in light of new developments, to ensure humane capital punishment. There is no reason to suppose that today’s decision will be any different.

(John G. Roberts Jr, Baze v. Rees, 553 U. S. ___ [2008] [brackets in original; footnote omitted])