What is the test for dismissing a juror in a criminal case?

We have held that, "[a] reviewing court should not disturb the trial judge's exercise of discretion in dismissing a juror unless there is a bias or prejudice to the defendant." United States v. Gambino, 951 F.2d 498, 503 (2d Cir. 1991) (internal quotation marks and citation omitted). "Prejudice in this context exists when the discharge is without factual support, or for a legally irrelevant reason." United States v. Purdy, 144 F.3d 241, 247 (2d Cir. 1998) (internal quotation marks and citations omitted).