How do we review the dismissal of a juror after deliberations have begun?

We review for abuse of discretion both the dismissal of a juror after deliberations have commenced and the denial of a motion for a new trial based on such a dismissal. United States v. Vartanian, 476 F.3d 1095, 1098 (9th Cir.2007) ; United States v. King, 660 F.3d 1071, 1076 (9th Cir.2011). The district court's factual findings relating to the issue of juror misconduct are reviewed for clear error. Vartanian, 476 F.3d at 1098. The decision to excuse a juror is committed to the district court's discretion and we must affirm unless we are left with the definite and firm conviction that the court committed a clear error of judgment in reaching its conclusion after weighing the relevant factors. United States v. Beard, 161 F.3d 1190, 1194 (9th Cir.1998) (quoting United States v. Egbuniwe, 969 F.2d 757, 761 (9th Cir.1992) (internal quotation marks omitted)).