On his first day on the bench as a U.S. Supreme Court justice, Brett Kavanaugh on Tuesday was not the most frequent questioner but showed he was fully prepared for the vexing ambiguities of a federal sentencing law—despite little time to get up to speed.

With his wife, two daughters and retired Justice Anthony Kennedy watching from special seats for guests of the justices, Kavanaugh, who was confirmed 50-48 by the Senate on Oct. 6 following a bruising confirmation process, appeared relaxed and engaged before and during two hours of oral arguments. Mike Davis, chief counsel to Senate Judiciary Chairman Chuck Grassley, who led the confirmation push, attended the argument.