Does a failure to object to improper argument waives any error?

We often have said that failure to object to improper argument waives any error. See, e.g., United States v. Potter, 616 F.2d 384, 393 n.16 (9th Cir. 1979), cert. denied, 449 U.S. 832, 101 S.Ct. 101, 66 L.Ed.2d 37 (1980). We review, if at all, because the misconduct sufficiently affects the trial to constitute plain error. United States v. Berry, 627 F.2d 193, 199 (9th Cir. 1980), cert. denied, 449 U.S. 1113, 101 S.Ct. 925, 66 L.Ed.2d 843 (1981). See also United States v. Singleterry, 646 F.2d 1014, 1018 (5th Cir. 1981); United States v. Cox, 633 F.2d 871, 875 (9th Cir. 1980), cert. denied, --- U.S. ----, 102 S.Ct. 159, 70 L.Ed.2d 130 (1981).

We reach the issue in this case because the trial judge denied West's mistrial motion on the merits rather than on its untimeliness. United States v. Dixon, 562 F.2d 1138, 1143 (9th Cir. 1977).