Brown v. United States, 602 U.S. 101

The Armed Career Criminal Act (ACCA) imposes a 15-year mandatory minimum for certain firearm offenders with three prior "serious drug offense" convictions.
ACCA defines a "serious drug offense" as a state offense involving a substance listed as a "controlled substance" under federal law, specifically as defined in the federal Controlled Substances Act (CSA).
Petitioners Brown (from Pennsylvania) and Jackson (from Florida) each received ACCA enhancements based on prior state drug convictions involving marijuana and cocaine, respectively.
After their state convictions but before their federal firearms charges were adjudicated, Congress amended the federal drug schedules, changing the definition of marijuana (exempting some hemp) and of cocaine (removing a medical derivative).
Both Brown and Jackson argued their prior convictions did not qualify as ACCA predicates because the relevant substances were defined differently by federal law at the time of their federal offenses or sentencing.

Issue	Brown's/Jackson's Arguments	U.S. Government Argument	Held
When must state and federal controlled substance definitions match for ACCA purposes?	Brown: At time of federal sentencing; Jackson: At time of federal firearms offense	At time of the underlying state conviction	Must match when the defendant committed the state crime
Should later changes in federal drug schedules retroactively impact ACCA predicate status?	Yes; later changes mean prior convictions don't count if definitions now differ	No; ACCA looks to substance schedules at time of state convictions	No; subsequent changes are irrelevant for ACCA predicate analysis
Does the categorical approach require matching the substance definitions at sentencing?	Yes; focus should be present schedules (current law)	No; the law at time of the prior conviction governs	No; categorical approach applies to elements at time of state conviction
Should rule of lenity apply due to statute ambiguity?	Yes; ambiguity should benefit defendants	Not applicable—statute is clear in context	No; context and precedent resolve any ambiguity

McNeill v. United States, 563 U.S. 816 (2011) (ACCA requires courts to examine the law as it existed when the defendant violated it; subsequent changes don't affect predicate status)
Shular v. United States, 589 U.S. 154 (2020) (categorical approach applies—state offense counts only if its elements necessarily match federal definitions)
Taylor v. United States, 495 U.S. 575 (1990) (explains ACCA's focus on certain kinds of recidivist offenders and approach to predicate crimes)
Mathis v. United States, 579 U.S. 500 (2016) (explains and applies the categorical approach for determining predicate offenses)