In the Pate v. Robinson case of 1965, the U.S. Supreme Court ruled that a defendant's constitutional rights were violated when he was not given a hearing on his competency to stand trial for murder charges despite substantial evidence suggesting he was mentally unfit. The court held that due process required such a hearing under the Fourteenth Amendment if there is reasonable cause to believe that the accused is incapable of understanding proceedings or assisting in their own defense. In this case, Wade Robinson had exhibited bizarre behavior and had been diagnosed with chronic paranoid schizophrenia prior to his trial but no competency hearing took place before or during it. The Supreme Court reversed Robinson’s conviction and ordered a new trial because it found that doubts about an accused person's mental capacity deprived him of fair treatment unless those doubts are resolved by procedures adequate to protect his rights.

In the Pate v. Robinson case, Justice Harlan dissented from the majority opinion. He argued that there was no constitutional error in how Illinois courts handled Robinson's claim of insanity during his trial for armed robbery. According to him, while it is true that due process requires a hearing on competency if substantial evidence raises doubt about a defendant's mental fitness, he did not believe such doubts were raised in this case. The defense counsel never requested a sanity hearing and even presented an alibi defense instead of an insanity one at trial; thus indicating they believed their client competent enough to stand trial and assist with his own defense. Furthermore, Justice Harlan pointed out that psychiatrists' reports indicated only potential emotional instability rather than clear-cut psychosis or incompetency which could have justified automatic triggering of a competency hearing without explicit request by the defense.