Trump will never get the majority of the delegates at the convention. His lead in the national polls would have to be way more than it is. People who actually participate in caucuses and primaries are very loyal to the party establishment. That's why a guy like McCain or Romney gets the support from those people. Those people listen to what the local precinct captain says, and those guys will be for Bush, Rubio, Cruz or Christie. Right now those guys are working out that decision, but they will coalesce soon.
