Law & psychiatry: Does the constitution require an insanity defense?

Idaho is one of four states that have abolished the insanity defense. Hence, John Delling, on trial for two murders in Idaho, was unable to plead insanity or to argue that he lacked intent to kill, the only available option under Idaho law. After being sentenced to life in prison without parole, Delling challenged the constitutionality of Idaho's law. The state's supreme court rejected his appeal, holding that--despite the long history of the insanity defense and its widespread acceptance--there was no constitutional right to an insanity defense. Delling's petition to the U.S. Supreme Court was turned away, leaving the constitutional status of the insanity defense uncertain.