States must use modern clinical tests to ensure those they wish to execute are not mentally disabled, the U.S. Supreme Court ruled today.

Adjudications of mental disability must be informed by the view of medical experts, and that instruction “cannot be sensibly read” to allow states to ignore medical consensus, Justice Ruth Bader Ginsburg wrote in a 5-3 opinion.

States may not execute the mentally disabled under Atkins v. Virginia, 536 U.S. 304 (2002). Bobby Moore challenged his death sentence on this basis, arguing that under modern clinical definitions, he qualified as disabled.

But the Texas Court of Criminal...