What is the test for excusing a prospective juror for their views on the death penalty?

"A prospective juror may be excused for cause if his or her views on capital punishment would ' "prevent or substantially impair the performance of his [or her] duties as a juror...." ' [Citations.] Where a prospective juror's responses are equivocal or conflicting, the trial court's assessment of the juror's state of mind is generally binding. Where there is no inconsistency, but simply a question whether the juror's responses demonstrated a bias for or against the death penalty, the trial court's judgment will not be set aside if it is supported by substantial evidence." (People v. Wash (1993) 6 Cal.4th 215, 254, 24 Cal.Rptr.2d 421, 861 P.2d 1107.)