His percent of the vote has minimally increased despite the limited field. Try again.
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It appears you are thinking about this in simplistic terms. I think you would agree that there are a lot of moving parts in this election cycle. But one thing is clear at this juncture: its highly likely that Trump will have a plurality of votes come convention time.
According to the tracking poll in the story below, a majority — 57 percent — of registered Republicans and Republican-leaners say that Trump should win the Republican nomination for president if he wins a plurality.
However, according to the same poll, if you support someone else then a small majority says he should not be the nominee. The point is, there is some complex political calculous underlying this nomination process. Its not as simple as just looking for a 50% number.
You’ll see other complications if you read the article. But however you look at it its remarkable that, in spite of a very large field of formidable contenders, that Trump has such a large lead. But as the Yogi Berra said, it ain’t over until its over.
Trump has had a golden opportunity in the last 4 weeks to appear more presidential and attempt to unite the party and he refuses to do so. My entire extended family is horrified of Trump and all but one claim they will never vote for him in November - they all love Cruz. On the other hand, if Cruz steals the nomination (playing by the rules established years ago), the nomination won't be worth having because most Trump supporters will sit out or worse vote for Hillary.
So the solution, is for Trump to start showing his strength, getting 50% or close to it in the remaining primaries, show an attempt to understand policy and actually speak to the issues in a way that conveys a decent level of cogency and not tweet about Megyn or Heidi.
These things are in Trump's control. If he can do these things, a lot of concern will fall away, and he can reassure those who are presently horrified about his candidacy. It will take discipline. Does Trump have any?