He can’t win with the voters, so he is ensuring he’ll win with the delegates. He doesn’t care that millions more people supported Trump. He wants this, and he will take it away at the convention if he has to.
When the outcome doesn’t fit what you want, find a technicality in the rules, claim that’s the best way to win and mock anyone who says differently. In short, whatever he does is the right thing. The lesson of the Left.