Does Rehaif error per se affect a defendant's substantial rights under the third prong of plain-error review?

QUESTION PRESENTED In Rehaif v. United States, this Court identified a new mens rea element of an offense under 18 U.S.C. § 922(g)(1), overturning “what was then the universal and long-established” interpretation that had been adopted “by every single Court of Appeals to address the question.” 139 S. Ct. 2191, 2194-98 (2019); id. at 2201-02 (Alito, J., dissenting). On direct appeal, the Ninth Circuit held that a trial court’s pre-Rehaif failure to instruct the jury on that previously unrecognized element was subject to a harmless-error analysis, even though the element had not been alleged in the indictment, presented to the jury at trial, or reasonably subject to challenge at trial before Rehaif overturned the law of every circuit. Does Rehaif error per se affect a defendant’s substantial rights under the third prong of plain-error review? i RULE 14.1(b) (iii) STATEMENT This case arises from the following proceedings in the United States District Court for the District of Arizona and the United States Court of Appeals for the Ninth Circuit: United States v. Romero-Salgado, No. (D. Ariz. Aug. 29, 2018); and United States v. Romero-Salgado, 796 F. App’x 346 (9th Cir. 2019). No other proceedings in state or federal trial or appellate courts, or in this Court, are directly related to this case. ii