President Trump pulled an inside straight to win in 2016, and now he needs another one. The good news for Trump is that his approval rating has stopped falling recently. The bad news is that it has stabilized in the low 40s. Election-watcher Harry Enten points out that no president since Harry Truman has won with anything like Trump’s negative net approval rating. Truman won at –6, while incumbents who lost (Gerald Ford, Jimmy Carter, and George H. W. Bush) averaged out at about –13, roughly where Trump’s number is. The presidents who won reelection averaged an approval rating of...