The second-best, but more likely, scenario is to deny Mr. Trump the 1,237 delegates required to automatically win on the first ballot. Right now, that seems quite doable. Recently, University of Virginia political scientist Larry Sabato projected the most likely scenario for Mr. Trump to get to 1,237. It required Mr. Trump to carry both Wisconsin and Indiana handily, and even then he only landed at 1,239. Right now, that looks unlikely. And if Mr. Trump loses just a couple congressional districts in Mr. Sabato's scenario, he'll fall short.