In Drope v. Missouri, the U.S. Supreme Court ruled in 1974 that a criminal defendant's right to due process is violated if his trial proceeds despite significant indications of his mental incompetence. The case involved Ronald Drope who was convicted for rape and sentenced to life imprisonment by a Missouri court even though he had attempted suicide during the course of his trial and there were other signs suggesting possible mental instability. His wife testified about his erratic behavior and history of impulsive violence, but no psychiatric evaluation was ordered by the court before proceeding with the trial or sentencing him. The Supreme Court held that these circumstances should have raised doubts about Drope’s competence to stand trial, thus requiring further inquiry into this matter as per constitutional standards set forth in Pate v Illinois (1966). Therefore, it reversed the judgment on grounds that failure to suspend proceedings under such conditions denied him fair opportunity to participate in his defense violating due process rights guaranteed by Fourteenth Amendment.

In the dissenting opinion for Drope v. Missouri, Justice William Rehnquist disagreed with the majority's view that a defendant's suicide attempt should automatically trigger an inquiry into his competency to stand trial. He argued that such a rule would unnecessarily delay trials and burden courts without significantly improving defendants' rights or welfare. Instead, he suggested that judges should have discretion in deciding whether to hold competency hearings based on all available evidence of a defendant’s mental state. Furthermore, he contended that there was no constitutional requirement for continuous monitoring of competence throughout trial proceedings as it could lead to unnecessary interruptions and complications during trials.