In United States v. Wallace, 848 F.2d 1464 (9th Cir. 1988), the Ninth Circuit explained how prosecutorial misconduct fits into a "cumulative error" analysis, stating: "Normally, a "cumulative error" analysis considers "all errors and instances of prosecutorial misconduct which were preserved for appeal with a proper objection or which were plain error." . . . The cumulative impact of several errors might therefore be sufficient to persuade us to grant review when the impact of each would not ... We may consider the prosecutorial vouching on cumulative error review." Wallace, 848 F.2d at 1476 n.2 . I In Wallace, the prosecutorial vouching was compounded by the fact that the conviction rested entirely on the uncorroborated testimony of co-conspirators. The Ninth Circuit noted with approval that sensitivity to cumulative error arises when the convictions are based on the largely uncorroborated testimony of a single accomplice or co-conspirator, such as cumulative errors that go to the credibility of the witnesses. See United States v. Hibler, 463 F.2d 455 (9th Cir. 1972).