Can a prospective juror's views about the death penalty "prevent or substantially impair" his duties as a juror?

As we [have] explained ..., `[w]hen a prospective juror's views about the death penalty "would `prevent or substantially impair the performance of his [or her] duties as a juror'" [citation], the juror is not impartial and may be challenged "for cause."'" (People v. Earp (1999) 20 Cal.4th 826, 853, 85 Cal.Rptr.2d 857, 978 P.2d 15.) This test applies equally to defense and prosecution challenges. (Ibid.) As stated, "`if the juror's statements are equivocal or conflicting, the trial court's determination of the juror's state of mind is binding. If there is no inconsistency, we will uphold the court's ruling if it is supported by substantial evidence. [Citations.]' [Citation.] A juror's bias need not `be proven with unmistakable clarity. [Citations.] Rather, it is sufficient that the trial judge is left with the definite impression that a prospective juror would be unable to faithfully and impartially apply the law in the case before the juror.'" (People v. Carpenter, supra, 21 Cal.4th 1016, 1035, 90 Cal.Rptr.2d 607, 988 P.2d 531.)