In Rosales-Lopez v. United States, 451 U.S. 182 (1981), the defendant, a Mexican-American, was charged with illegally bringing Mexican nationals into the United States. The Supreme Court held that a federal court must inquire about racial prejudice, not in all cases, but only in cases where the defendant was accused of a violent crime and the defendant and the victim were members of different racial or ethnic groups. Absent such circumstances, the Constitution leaves it to the trial court's discretion to determine the need for such questions. Rosales-Lopez, 451 U.S. at 184-94. The Court gave its blessing to what amounts to a form of harmless error review in situations where the trial court, in conducting voir dire, fails to ask prospective jurors questions about racial or ethnic prejudice as requested by a defendant who is a member of a minority group. The court rejected a reversal per se rule adopted in some circuits in favor of one that requires the trial court to pose such questions only where there is some indication the particular case is likely to have racial overtones or involve racial prejudice. ( Id. at pp. 188-189.) The court recognized that voir dire serves a "critical function" in protecting a defendant's Sixth Amendment right to an impartial jury. It noted, among other things, that a "lack of adequate voir dire impairs the defendant's right to exercise peremptory challenges where provided by statute or rule . . . ." ( Rosales-Lopez v. United States, supra, 451 U.S. at p. 188.) Nonetheless, the court held a failure to examine prospective jurors about racial prejudice assumes constitutional proportions (and requires reversal on that ground) only where "special circumstances" exist, and the indications racial prejudice is likely to affect the jurors in the particular case are "substantial." ( Id. at pp. 189-190.)