In Kahler v. Kansas, No. 18-6135 (March 23, 2020), a divided United States Supreme Court held that the Due Process Clause does not require Kansas to adopt an insanity test that turns on a defendant’s ability to recognize that his crime was morally wrong. In other words, Due Process does not compel States to adopt the moral-incapacity test from the landmark M’Naghten’s Case, 10 Cl. & Fin. 200, 8 Eng. Rep 718 (H.L. 1843).
M’Naghten's Case famously recognized two alternative pathways to acquittal based on insanity: (1) the moral incapacity test—whether a defendant’s mental illness left him unable to distinguish right from wrong; and (2) the cognitive incapacity test—whether defendant was able to understand what he was doing when he committed a crime. Under Kansas law, a defendant may only raise mental illness to show that he “lacked the culpable mental state required as an element of the offense charged,” although he can present additional mental health evidence at sentencing.
The 6 to 3 majority opinion in Kahler was delivered by Justice Kagan, joined by Chief Justice Roberts and Justices Thomas, Alito, Gorsuch, and Kavanaugh. The majority reaffirmed that a Due Process challenge to “a state rule about criminal liability—laying out either elements of or the defenses to a crime—violates due process only if it ‘offends some principle of justice so rooted in the traditions and conscience of our people as to be ranked as fundamental.’” Looking to historical practice as a guide, the majority reaffirmed that (within broad limits) doctrines of criminal responsibility, such as the contours of the insanity defense, must remain the province of the states. The Court recognized continuing division over the proper scope of the insanity defense and the “uncertainties of the human mind.” As Justice Kagan explained:
Defining the precise relationship between criminal culpability and mental illness involves examining the workings of the brain, the purposes of the criminal law, the ideas of free will and responsibility. It is a project demanding hard choices among values, in a context replete with uncertainty, even at a single moment in time. And it is a project, if any is, that should be open to revision over time, as new medical knowledge emerges and as legal and moral norms evolve. Which is all to say that it is a project for state governance, not constitutional law.
Justice Breyer filed a dissenting opinion joined by Justices Ginsburg and Sotomayor. Briefing on the merits is available at the Supreme Court’s website here.
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