Trump might end up a spoiler, staying on the ballot for the fun of it, and getting enough delegates to prevent anyone else from crossing the 50 percent threshhold.
There are several scenarios.
It requires that the top candidate not get 50 percent of pledged delegates. The main way I see that happening is if there's a clash between two frontrunners, with a third candidate getting some support. Huckabee or Rand Paul could easily fit that role, since they could have a strong base of support.
It is a bit unlikely, though.
The establishment would unite if somone they consider unacceptable is leading in the polls.
With Hillary and Obama in 2008, there was more of a cultural divide. It was about experience and the possibility of the first female President versus change, youth and the possibility of the first African-American President. I don't see Republicans getting as passionate about likely match-ups (Bush VS Rubio, Rubio VS Walker, Bush VS Walker.) There's likely to be a point where the frontrunner pulls away.
If the top 2 candidates are over 50%, it's all over.
If candidate 2 and 3 are over 50%, it's all over.
We haven't seen a primary in which the top candidate failed to get 50% in over a generation, so we really don't know what'll happen, especially with multiple candidates acceptable to the establishment.
