The Armed Career Criminals Act provided for enhanced mandatory minimum sentences for individuals who possessed a firearm after being convicted of three or more violent or drug-related felonies. Under the act, a qualifying felony included one that involved conduct that presented a serious potential risk of physical injury to another. In Johnson v. United States, 135 S. Ct. 2551 (2015), the Supreme Court held this particular provision in the act void for vagueness. Gregory Welch (defendant) was sentenced under the act’s invalidated provision before the Supreme Court’s ruling in Johnson. Welch filed a collateral motion challenging his sentencing, arguing that Johnson should apply retroactively. The United States (plaintiff) agreed that Johnson should apply retroactively. The district court denied the motion. The court of appeals affirmed. The United States Supreme Court granted certiorari.