The Justice Department is defending its prosecution of a man for owning a gun despite regularly using marijuana. Does that violate the Second Amendment?

The Supreme Court seemed likely Monday to loosen a federal law that bars marijuana users from owning guns in a case that crossed typical political lines.

Cecillia Wang, legal director at the ACLU, said the law violates the Second Amendment and is unconstitutionally vague about what it means to be a drug user.