What is the legal test for disqualification of a judicial officer?

The presumption of impartiality may "be overcome only by specific evidence demonstrating actual bias or a particular combination of circumstances creating an unacceptable risk of bias." ( Morongo Band, supra , 45 Cal.4th at p. 741, 88 Cal.Rptr.3d 610, 199 P.3d 1142.) The mere appearance of bias, however, is not a ground for the disqualification of a judicial officer. ( Andrews v. Agricultural Labor Relations Bd. (1981) 28 Cal.3d 781, 791, 171 Cal.Rptr. 590, 623 P.2d 151.)³³ To disqualify a judicial officer, the moving party must offer legally sufficient facts to demonstrate the judicial officer's bias, which must be " against a particular party [citations] and sufficient to impair the judge's impartiality so that it appears probable that a fair trial cannot be held. " ( Id. at p. 792, 171 Cal.Rptr. 590, 623 P.2d 151.) If that burden is satisfied, "the challenged judicial officer or a reviewing court must still decide whether such bias will render it probable that a fair trial cannot be held before that judge. In other words, the bias or prejudice must be sufficient to impair the judge's impartiality. " ( Ibid. )