That poll was a South Carolina perspective. The national polling has Trump, Cruz, Rubio in the
70% range with less than 30% split amongst the others. Trump about 10% in the lead among those
three. Nationally it is close but statewides are showing different.
As the contest goes on and the RNC/GOPe keeps losing, the loser’s supporters will either get on board with Trump, or lose the motivation to go vote. Is “PLEASE, WE NEED A BROKERED CONVENTION!! YEAH!” a great rallying cry? Once there are 6-10 contests out of the way where no GOPe candidate can beat Trump and/or crack 15%, their numbers are going to start to plummet. Only hardcore establishment types will be foaming at the mouth for a brokered convention at that point; average voters are going to give up and go back to the business of carrying on with their lives.