Karen Kahler filed for divorce from D and moved out of their home with their two teenage daughters and 9-year-old son. D became more and more distraught. D drove to the home of Karen’s grandmother and entered through the back door and saw Karen and his son. He shot Karen twice while allowing his son to flee the house. He then moved through the residence, shooting Karen’s grandmother and each of his daughters in turn. All four of his victims died. D surrendered to the police the next day and was charged with capital murder. D filed a motion arguing that Kansas’s treatment of insanity violates the Fourteenth Amendment’s Due Process Clause; Kansas had “unconstitutionally abolished the insanity defense” by allowing the conviction of a mentally ill person “who cannot tell the difference between right and wrong.” The trial court denied the motion. The jury convicted D of capital murder. At the penalty phase, the court permitted D to offer additional evidence of his mental illness and to argue in whatever way he liked that it should mitigate his sentence. The jury imposed the death penalty. D appealed and the Kansas Supreme Court rejected his Due Process argument. The court found that “due process does not mandate that a State adopt a particular insanity test.” The insanity defense was not so ingrained in our legal system as to count as fundamental. D appealed. D asked this Court to decide whether the Due Process Clause requires States to provide an insanity defense that acquits a defendant who could not “distinguish right from wrong” when committing his crime-or, otherwise put, whether that Clause requires States to adopt the moral-incapacity test from M’Naghten.