In Kahler v. Kansas, 140 S. Ct. 1021 (2020), the U.S. Supreme Court recently held that the Due Process Clause of the U.S. Constitution does not require a state to adopt a particular formulation of the insanity defense. The ruling came in a case out of Kansas where the state had adopted the "cognitive incapacity" test, which examines whether a defendant was able to understand what he was doing when he committed the crime. The Kansas statute does not incorporate the "moral incapacity" test, which is the inquiry into whether a defendant could not distinguish right from wrong when committing the crime. The defendant contended that the state's failure to allow a defendant to raise a defense based on "moral incapacity" violated due process. The Court rejected such argument, holding that a state's insanity rule was substantially open to state choice. In so holding, the Court cited to Clark v. Arizona, 548 U.S. 735 (2006), where it had catalogued the diverse strains of the insanity defense that states have adopted to absolve mentally ill defendants of criminal responsibility. The dissent agreed that states were free to provide different definitions and standards related to the insanity defense but found that Kansas did not simply redefine the insanity defense; rather, it eliminated the core of a defense that has existed for centuries.