The dashing of Beto O'Rourke's presidential hopes can be traced, in our estimation, to one moment of truth. It wasn't his tendency to flap his arms, say, or his radical green agenda or his claim that he was born to be in the political fray, unconvincing as all those might be. It was his vow after the mass shooting at El Paso. "Hell yes," he shouted during the Democratic debate in Houston, "we're going to take your AR-15." It happens that we were watching the debate live when Mr...
