The rule against racially discriminatory use of peremptory challenges is one of the very few constitutional rules of criminal procedure that applies equally to the defense and prosecution.  See Georgia v. McCollum, 505 U.S. 42 (1992). So what happens on appeal when a trial judge denies a defense challenge of a juror under McCollum, but the appellate court decides the challenge was valid?

It is well established that in the reverse situation, when a juror is discriminatorily struck who should have been seated, the error is reversible per se. No "harmless error" analysis is allowed. What about a juror who is not challengeable for cause and meets the legal qualifications, but whom the defense should have been allowed to strike under the state-law peremptory challenge procedure? That is the question decided in in Rivera v. Illinois, announced today.

The right to exercise peremptory challenges in state court is determined by state law. This Court has "long recognized" that "peremptory challenges are not of federal constitutional dimension." United States v. Martinez-Salazar, 528 U. S. 304, 311 (2000). States may withhold peremptory challenges "altogether without impairing the constitutional guarantee of an impartial jury and a fair trial." Georgia v. McCollum, 505 U. S. 42, 57 (1992). Just as state law controls the existence and exercise of peremptory challenges, so state law determines the consequences of an erroneous denial of such a challenge. Accordingly,we have no cause to disturb the Illinois Supreme Court's determination that, in the circumstances Rivera's case presents, the trial court's error did not warrant reversal of his conviction.

Justice Ginsburg wrote the opinion for a unanimous court. Her opinion goes on to reject the perennial attempt to transform an error of state law into a violation of the Due Process Clause of the Fourteenth Amendment.