When the definitive history of Donald Trump’s presidency is written, it’ll likely begin on April 30, 2011, long before he was actually elected. That’s when Seth Meyers, then the anchor of “Weekend Update” on “Saturday Night Live,” told a joke that, some believe, so infuriated Trump he resolved to run for president. Speaking at the White House Correspondents' Dinner that night, Meyers acknowledged Trump in the audience, and then said: “Donald Trump has been saying he will run for president as a Republican, which is surprising, since I just assumed he was running as a joke.” It got a big...