What is the test for determining whether a defendant is mentally competent to stand trial?

mental condition is such that he lacks the capacity to understand the nature and object of the proceedings against him, to consult with counsel, and to assist in preparing his defense." United States v. Kerr, 752 F.3d 206, 215 (2d Cir. 2014) (internal quotation marks and citation omitted).

A district court must "order a hearing" either on motion or "sua sponte to determine the mental competence of a defendant 'if there is reasonable cause to believe that the defendant may presently be suffering from a mental disease or defect rendering him mentally incompetent.'" United States v. Quintieri, 306 F.3d 1217, 1232 (2d Cir. 2002) (emphasis added) (quoting 18 U.S.C. 4241(a)). To aid in its competency assessment, the district court "may order that a psychiatric or psychological examination of the defendant be conducted." 18 U.S.C. 4241(b). As this permissive language makes plain, a district court need not order a psychological examination whenever the defendant's competency to stand trial is questioned. A court may assess the need for a competency hearing based "on [its] observation of the defendant during the proceedings." United States v. Vamos, 797 F.2d 1146, 1150 (2d Cir. 1986); see also, e.g., United States v. Sovie, 122 F.3d 122, 128 (2d Cir. 1997) (affirming the denial of a psychiatric examination where the district court personally observed the defendant participate in his defense). "Whether 'reasonable cause' to hold a hearing exists is a highly particularized assessment that 'varies in each case.'" DiMartino, 949 F.3d at 71 (quoting United States v. Zhou, 428 F.3d 361, 379 (2d Cir. 2005)).¹