President Obama brusquely cut off a reporter’s question Thursday about Hillary Clinton’s use of a private email system at the State Department. At a press conference in Japan, the president said he would take one more question from reporters. But when the question turned out to be about Mrs. Clinton’s emails that violated State Department rules, he quickly changed his mind. “You know I take it back — I’m not taking another question,” Mr. Obama said. “We’re in Japan, don’t you have something to do with Asia that we want to talk about? I’ll be talking about this in Washington...