Rule 614(b) of the Federal Rules of Evidence expressly permits judges to question witnesses. Judges may do so repeatedly and aggressively to clear up confusion and manage trials or where 'testimony is inarticulately or reluctantly given.' United States v. Norris, 277 U.S. App. D.C. 262, 873 F.2d 1519, 1525-26 (D.C. Cir. 1989) (upholding judge's participation in questioning defendant, although perhaps more extensive than it should have been, because it aimed at clarifying evidence) (quoting United States v. Barbour, 137 U.S. App. D.C. 116, 420 F.2d 1319, 1321 (D.C. Cir. 1969)).
District court authority to question witnesses and manage trials, however, has limits. Because juries, not judges, decide whether witnesses are telling the truth, and because judges wield enormous influence over juries, judges may not ask questions that signal their belief or disbelief of witnesses. United States v. Wyatt, 143 U.S. App. D.C. 136, 442 F.2d 858, 859-61 (D.C. Cir. 1971) (court's questioning of defendant and his alibi witnesses damaged defendant's credibility and therefore was reversible error). Because such questions can usurp the jury's factfinding function, cast the judge in the role of advocate, and 'breach [] the atmosphere of judicial evenhandedness that should pervade the courtroom,' ...