The republican nomination is really confusing me. Trump is going to win the popular vote. This is just a fact. He is also going to get the most delegates....another fact. Even if he doesn't get the magic number, why on earth would the republican establishment not just try and back (and win over) Trump? You are pretty much stuck with Cruz or Trump (neither of which will be as controllable as guys like Jeb please clap Bush, Marco Rubio, Scott Walker etc...). If Trump gets the most delegates and votes and he doesn't get the nomination you are going to piss off a good 1/3-1/4 of the voting base. Even if he doesn't go 3rd party, all the Bernie or busters in the world wouldn't stop Hillary from becoming president (or Bernie cuz I'm still clinging to his slim chances )
It's dangerous to view "The Republican Establishment" as a monolithic entity. It's not like Reince Priebus, the Koch brothers, Rupert Murdoch, and Jeb! all get in a room and pick the nominee (although it would probably make them all happy if that's how it works). The Republican establishment is a combination of elected officials at every level, the state Republican committees, the right wing media, the rank and file voters that dedicate time campaigning, et cetera. Each of these have different interests.
A plurality of the voters want Trump, so most pledged delegates go to Trump. Most Trump voters are not members of the political establishment in any sense of the word; Cruz on the other hand is much more savvy to the inner workings of the process and thus has the infrastructure to win at the delegate selection process, so a lot of the delegates will support him in later ballots. The punditocracy, the Acelas, the high up elected officials all hate both of course, but the rank-and-file unilaterally rejected Walker-Bush-Rubio. If this was the 1950s, then that would be the political establishment. But the establishment is more expansive than that, so it's unlikely any rabbits will be pulled out of hats.