Jeannine Pirro, the U.S. attorney for the District of Columbia, on Monday threatened jail time for anyone who enters the capital with a gun. In remarks on Fox News that could deepen a growing rift between gun owners and the Trump administration, Ms. Pirro declared that if anyone brings “a gun into the District, you mark my words, you’re going to jail. I don’t care if you have a license in another district and I don’t care if you’re a law-abiding gun owner somewhere else.” Her remarks prompted swift pushback from the Republican Party’s pro-Second Amendment wing, which was thrown...