Donald Trump has a habit of grossly exaggerating his popular support, particularly his performance in elections. This had famously pernicious effects in 2020: He refused to accept defeat, claiming not just that he won but that he “won by historic numbers,” and tried to overturn the results with the help of a mob that assaulted the Capitol. But it came as no real surprise, since in 2016 he couldn’t be satisfied with an Electoral College victory, instead...