United States v. Dat Do, 994 F.3d 1096

While driving on the Warm Springs Indian Reservation, Dat Quoc Do fired six shots into the air at another vehicle after a passenger threw a plastic bottle at his girlfriend’s car.
Do was charged in federal court under the Assimilative Crimes Act (ACA) with two counts based on Oregon’s unlawful use of a weapon (UUW) statute, rather than under the federal assault statute.
Do moved to dismiss, arguing the federal assault statute precluded assimilation of Oregon’s UUW; the district court denied the motion, and a jury convicted Do on both UUW counts.
The district court sentenced Do to three years’ probation; Do appealed.
The Ninth Circuit applied the Lewis two-step ACA test and held Do’s conduct was punishable under the federal assault statute and that the federal statute precluded assimilation of Oregon’s UUW (because it punished the same behavior, occupied the field, and assimilation would rewrite federal offense definitions).
The court reversed Do’s convictions and remanded for proceedings consistent with that holding.

Issue	Gov't Argument	Do's Argument	Held
1) Was Do’s conduct made punishable by any enactment of Congress?	Yes — federal assault statute (§ 113) covers his conduct (simple assault and assault with a dangerous weapon).	Agreed (no dispute).	Yes — federal assault statute punishes Do’s conduct.
2) Does the federal assault statute preclude assimilation of Oregon’s UUW under the ACA?	No — UUW targets weapon use and fills a gap; different focus and higher penalties.	Yes — UUW and federal assault punish approximately the same assaultive conduct.	Precluded — federal statute bars assimilation.
3) Does the federal assault statute occupy the field of assault so as to exclude state offenses?	No — the statutes are different in form/label and UUW is not labeled an assault statute.	Yes — federal § 113 is comprehensive and evidences intent to occupy the field.	Yes — § 113’s comprehensive scope reveals congressional intent to occupy the field.
4) Would assimilating Oregon’s UUW effectively rewrite Congress’s offense definitions or allow circumvention of federal sentencing choices?	No — use of state statute is permissible to punish weapon misuse.	Yes — UUW’s lower mens rea and higher maximum (5 years) would let prosecutors obtain greater punishment than federal law (simple assault max 6 months) without proving § 113(a)(3) intent.	Yes — assimilation would impermissibly alter Congress’s scheme and permit prosecutors to bypass federal sentencing choices.

Lewis v. United States, 523 U.S. 155 (1998) (establishes ACA two-step test and purpose: borrow state law to fill gaps in federal enclave criminal law)
United States v. Rocha, 598 F.3d 1144 (9th Cir. 2010) (federal assault statute’s comprehensive definitions show intent to occupy the field of assault)
United States v. Souza, 392 F.3d 1050 (9th Cir. 2004) (discusses when federal law precludes assimilation under Lewis)
United States v. Waites, 198 F.3d 1123 (9th Cir. 2000) (state law precluded where it punishes the same wrongful behavior as federal regulation)
United States v. Lewellyn, 481 F.3d 695 (9th Cir. 2007) (federal assault statute incorporates common-law assault definitions)
United States v. Smith, 925 F.3d 410 (9th Cir. 2019) (confirms ACA applies in Indian country)