Imagine a President of the United States who’s a loose cannon, an impulsive creature of pure id barely held back from the brink of disaster by the various women tasked with keeping him out of trouble. That hypothetical scenario might not be quite as hard to imagine as it once was. And yet the titular figure at the center of “POTUS: Or, Behind Every Great Dumbass Are Seven Women Trying to Keep Him Alive” is left to the imagination, unseen and unnamed. Scrambling to do damage control during a diplomatic debacle are the President’s chief of staff, press secretary, first...