What is the test for a motion of no confidence in a federal district judge?

The principal claim made by appellants is that they were deprived of a fair trial and of effective assistance of counsel by statements and actions of the trial judge during the course of the two-week trial. In considering this claim we are guided by the principle that while the district judge "is more than a moderator or umpire and has an active responsibility to see that a criminal trial is fairly conducted," United States v. Curcio, 279 F.2d 681, 682 (2d Cir.), cert. denied, 364 U.S. 824, 81 S.Ct. 59, 5 L.Ed.2d 52 (1960), his "participation during trial-whether it takes the form of interrogating witnesses, addressing counsel, or some other conduct-must never reach the point at which it appears clear to the jury that the court believes the accused is guilty," United States v. Nazarro, 472 F.2d 302, 303 (2d Cir. 1973).