What is the test for a defendant to be competent to stand trial?

It is well established that "a person whose 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 may not be subjected to a trial." Drope v. Missouri, 420 U.S. 162, 171 (1975). To be competent to stand trial, a defendant must have "a rational as well as factual understanding of the proceedings against him." Godinez v. Moran, 113 S.Ct. 2680, 2685 (1993) (internal quotation marks omitted). The trial court must be alert to circumstances suggesting that the accused is unable to meet the standards of competence and must order a hearing on competency "if there is reasonable cause to believe that the defendant may presently [be incompetent]," 18 U.S.C. 4241(a).