Constitution Does Not Require Morality-Based Insanity Defense

The U.S. Supreme Court today rejected the claim that the Constitution requires a State to recognize an insanity defense based on the defendant’s inability to know his conduct is wrong. It is sufficient, if a State so chooses, to limit the defense to the defendant’s inability to know what he was doing. Justice Elena Kagan wrote the opinion of the Court in Kahler v. Kansas, No. 18-6135.

This case is about Kansas’s treatment of a criminal defendant’s insanity claim. In Kansas, a defendant can invoke mental illness to show that he lacked the requisite mens rea (intent) for a crime. He can also raise mental illness after conviction to justify either a reduced term of imprisonment or commitment to a mental health facility. But Kansas, unlike many States, will not wholly exonerate a defendant on the ground that his illness prevented him from recognizing his criminal act as morally wrong. The issue here is whether the Constitution’s Due Process Clause forces Kansas to do so—otherwise said, whether that Clause compels the acquittal of any defendant who, because of mental illness, could not tell right from wrong when committing his crime. We hold that the Clause imposes no such requirement.

Justice Breyer dissented, joined by Justices Ginsburg and Sotomayor.

Like the Court, I believe that the Constitution gives the States broad leeway to define state crimes and criminal procedures, including leeway to provide different definitions and standards related to the defense of insanity. But here, Kansas has not simply redefined the insanity defense.Rather, it has eliminated the core of a defense that has existed for centuries: that the defendant, due to mental illness, lacked the mental capacity necessary for his conduct to be considered morally blameworthy. Seven hundred years of Anglo-American legal history, together with basic principles long inherent in the nature of the criminal law itself,convince me that Kansas’ law “ ‘offends . . . principle[s] of justice so rooted in the traditions and conscience of our people as to be ranked as fundamental.’ ” Leland v. Oregon, 343 U. S. 790, 798 (1952) (quoting Snyder v. Massachusetts, 291 U. S. 97, 105 (1934)).