A day after the U.S. Supreme Court took up Arizona’s tough immigration laws, a Republican senator grilled Ninth Circuit U.S. Court of Appeals nominee Paul Watford on his firm’s work on the case.

Under questioning led by Sen. Chuck Grassley, the ranking minority member of the Judiciary Committee, Watford explained various arguments made in a suit in which his firm, Munger, Tolles & Olson, represented a coalition of civil rights groups challenging the state laws. (Click here for video of the hearing.)