Congress enacted a federal law criminalizing the conduct of one who “uses or carries a firearm” while trafficking drugs. Muscarello (defendant) was convicted of carrying a firearm in the locked glove compartment of his vehicle while involved in a drug trafficking crime. The court of appeals affirmed. Muscarello challenged the lower court’s interpretation of the law, arguing that the term “carries a firearm” applies only to a person who actually possesses a firearm on his person and not to one who possesses a firearm in his vehicle. The United States Supreme Court granted certiorari and consolidated a similar case.