Alabama executed Kenneth Eugene Smith with nitrogen gas in January 2024, the first such execution in American history. State attorneys promised Smith would lose consciousness in seconds, but witnesses reported he appeared awake for several minutes and "shook and writhed" for at least four minutes. The UN High Commissioner for Human Rights said the method "may amount to torture." Louisiana, Mississippi, and Oklahoma legalized nitrogen executions anyway.
The 8th Amendment bans cruel and unusual punishment, but the Supreme Court ruled in Trop v. Dulles that "cruel and unusual" changes over time. The test looks to "the evolving standards of decency that mark the progress of a maturing society." This doctrine fundamentally changed constitutional interpretation—punishments acceptable at ratification in 1791 might violate the 8th Amendment today. The Court has used evolving standards to ban executing juveniles and people with intellectual disabilities, reasoning that contemporary society views these groups as less culpable than adult criminals.