The narrow Trump defeat Henry Olsen expects would be just about the worst possible result from the standpoint of Republican unity. It would set up a protracted, bitter struggle in which Trump’s fans blame anti-Trump conservatives for electing Hillary Clinton while those conservatives blame Trump’s fans for helping to nominate someone they couldn’t in good conscience support and who polled worse than everyone else in the field. It would give Trump himself reason to think that he has a shot in 2020, and thus, compared to a big defeat, prolong his divisive presence in Republican presidential politics.