By the end of June 2020, the U.S. Supreme Court will have ended its latest term, which included several notable criminal law cases. In a decision dated March 23, 2020, the Court ruled that the Due Process Clause of the Fourteenth Amendment does not require states to offer a specific formulation of the insanity defense for criminal defendants, as long as some form of the defense is available. At issue in Kahler v. Kansas was the insanity defense in Kansas, which allows criminal defendants to argue that they cannot be convicted because they “lacked the culpable mental state required as an element of the offense charged,” Kan. Stat. Ann. §21–5209 (2018 Cum. Supp.).
This formulation is a variant of one prong of the traditional two-pronged approach to the insanity defense, most famously expounded in M’Naghten’s Case, (1843) 8 Eng. Rep. 718; 10 Cl. & Fin. 200, the landmark English decision from 1843. Under M’Naghten’s two prongs, a defendant could not be found guilty of a criminal offense if: 1) his mental incapacity made him unable to understand what he was doing when he committed a crime; or 2) his mental state made him unable to understand that his action was wrong. To take an example from Justice Breyer’s dissent,1 under the first prong, the defendant shot and killed a person whom he believed, due to his mental incapacity, was a dog. Under the second prong, he shot and killed a person, believing he was commanded to do so by a dog. Kansas allows the first defense, insofar as the defendant’s mental incapacity prevents him from forming the required mens rea to commit a crime. However, Kansas law does not allow a defendant to invoke the second M’Naghten prong, meaning James Kahler could not present a defense that his mental incapacity prevented him from understanding that his actions were wrong.
Kahler argued that not allowing him to rely on the second M’Naghten prong violated the Due Process Clause, because this defense is “so entrenched in the central values of our legal system” as to be fundamental to the system. The Court disagreed. In an opinion authored by Justice Kagan, and joined by the Chief Justice and Justices Thomas, Alito, Gorsuch, and Kavanaugh, the Court held that states have the freedom to decide what formulation of the various insanity defenses may be invoked in their courts. Indeed, the Court cited Clark v. Arizona, 548 U. S. 735, 749 (2006), in which the Court upheld Arizona’s law that allowed a defendant to argue the second M’Naghten prong as a defense, but not the first. Reaching beyond its own precedent in Clark, the Court then traced the development and historical variations of the insanity defense, from its origins in English Common Law to its diverse forms in the United States today. Such a varied history showed that some form of mental incapacity defense did appear fundamental to our justice system, but the defense need not necessarily include the second M’Naghten prong.
Kansas allows criminal defendants to present a mental incapacity defense, which Kahler did. It also allows defendants to present evidence of mental incapacity at the sentencing phase of a trial, where a defendant has wide latitude to decide how to present mental incapacity evidence. These options, the Court held, are enough to satisfy the requirements of due process.
1 Justice Breyer, joined by Justices Ginsburg and Sotomayor, dissented from the majority opinion, arguing that Kansas’s law departed enough from traditional forms of the insanity defense to violate due process.
