“When I imagine him in the White House, I’m disgusted,” declared a Hillary Clinton campaign email that went out May 4, just after Donald Trump clinched the Republican presidential nomination. The putative author, deputy communications director Christina Reynolds, explained her reaction wasn’t just to Trump’s policy ideas, yucky as they are, “but also because I try and imagine him doing the more symbolic, but often just as powerful, parts of the president’s job.”

She tried, and she failed: “I just can’t imagine him mourning...