Whether an appellate court may relieve a government party of its burden to show that a favorable error is harmless, decide the issue sua sponte, and thereby assume the government party's burden itself

QUESTIONS PRESENTED Here, the United States failed to argue that the lack of proper notice to Petitioner Jason Dix of a new theory for applying a sentencing enhancement was harmless error. Nevertheless, the United States Court of Appeals for the Fourth Circuit held that it was compelled to raise and decide harmless error sua sponte. There is general agreement that government parties bear the burden to show that favorable errors are harmless. Federal and state courts divide, however, on whether and when they may raise and decide harmless error sua sponte if a government party fails to raise the issue in its appellate briefing. L May an appellate court, consistent with due process, relieve a government party of its burden to show that a favorable error is harmless, decide the issue sua sponte, and thereby assume the government party’s burden itself? I. If appellate courts may assume a government party’s burden to show that a favorable error is harmless, is doing so mandatory or discretionary? Ill. If doing so is discretionary, what limitations do due process or other considerations place on when appellate courts may exercise that discretion and when appellate courts should exercise that discretion?