What standard of proof must the government meet to prove a preserved Guidelines error is harmless?

QUESTION PRESENTED The U.S. Sentencing Guidelines “are not only the starting point for most federal sentencing proceedings but also the lodestar.” Molina-Martinez v. United States, 578 U.S. 189, 200 (2016). Thus, even when a defendant fails to object to an erroneous Guidelines range at sentencing—and regardless of whether the “ultimate sentence falls within the correct range—the error itself can, and most often will, be sufficient to show a reasonable probability of a different outcome absent the error.” Id. at 198 (emphasis added). The question presented here has divided the courts of appeals for decades: By what standard of proof must the government prove that a Guidelines error is harmless when, unlike in Molina-Martinez, the defendant objected to the erroneous Guidelines range before the district court? i