“Hydraulic or magnets?” US President Donald Trump asked some baffled American troops stationed in Japan during his visit this week, and demanded to know which was better. That was during a speech aboard the USS George Washington, before hundreds of American servicemen and women who appeared to have no idea what their commander-in-chief was talking about. “You know, the new thing is magnets. So instead of using hydraulic that you can be hit by lightning and it’s fine, you take a little glass of...