In Medina v. California (1992) 505 U.S. 437, the United States Supreme Court upheld the California Supreme Court decision in People v. Medina, supra, 51 Cal.3d 870, finding: "Petitioner further contends that the burden of proof in competency proceedings should be placed on the State because we have allocated the burden to the State on a variety of other issues that implicate a criminal defendant's constitutional rights. The decisions upon which petitioner relies, however, do not control the result here, because they involved situations where the government sought to introduce inculpatory evidence obtained by virtue of a waiver of, or in violation of, a defendant's constitutional rights. In such circumstances, allocating the burden of proof to the government furthers the objective of 'deterring lawless conduct by police and prosecution.' No such purpose is served by allocating the burden of proof to the government in a competency hearing. In light of our determination that the allocation of the burden of proof to the defendant does not offend due process, it is not difficult to dispose of petitioner's challenge to the presumption of competence imposed by 1369, subd. (f). Under California law, a defendant is required to make a threshold showing of incompetence before a hearing is required . . . .In rejecting this contention below, the California Supreme Court observed that 'the primary significance of the presumption of competence is to place on defendant . . . the burden of rebutting it' and that, 'by its terms, the presumption of competence is one which affects the burden of proof.' We see no reason to disturb the California Supreme Court's conclusion that, in essence, the challenged presumption is a restatement of the burden of proof, and it follows from what we have said that the presumption does not violate the Due Process Clause."