To decide competency to stand trial, a district court must determine whether 'the defendant is presently suffering from a mental disease or defect rendering him mentally incompetent to the extent that he is unable to understand the nature and consequences of the proceedings against him or to assist properly in his defense.' 18 U.S.C. § 4241(d). While ''a district court's determination of competency to stand trial may not be set aside on review unless it is clearly arbitrary or unwarranted,'' United States v. Birdsell, 775 F.2d 645, 648 (5th Cir. 1985) (quoting United States v. Hayes, 589 F.2d 811, 822 (5th Cir. 1979)), an appeals court 'should take a hard look at the trial judge's ultimate conclusion and not allow the talisman of clearly erroneous to substitute for thoroughgoing appellate review of quasi-legal issues.' United States v. Makris, 535 F.2d 899, 907 (5th Cir. 1976); see also Birdsell, 775 F.2d at 648.