It’s not just the “establishment” that dislikes Trump. Lots of rank and file GOP voters do too.
And, since there’s a good chance he’s the candidate, the establishment should stop the attacks unless they prefer Hillary. Even if Cruz ends up the candidate it won’t hurt to have supported Trump for the last few months of the primaries.
Newsflash, the uniparty has preferred Hillary from the beginning of this season's election charade. Jeb was the designated RNC loser. The RNC does not want to win the presidency in this cycle. It will oppose a strong candidate, and let a weak one be skewered by the DEMs.
The Establishment elite RINOs do want Hillary as POTUS because they think they can keep their power, perks, and influence. They are all about the status quo with the Donkeys of the Washington, DC Unipoarty cabal.