It looks to me like the Bush wing are the main holdouts, while the rest of the GOP can see the handwriting on the wall. Witness yesterday where Rubio made peace overtures while Jeb was still trash talking.
My personal theory is that the Bushes have a lot they want to keep hidden, as do the Clintons of course, and both dynasties would rather have Hillary in the White House protecting their secrets than Trump in there exposing everything.
Remember how a big bunch of Bushistas glommed onto the Cruz campaign the minute Rubio crashed and burned? I think they’re the ones trying their best to keep Cruz in this until a contested convention, knowing full well the end result of that is a Hillary presidency.
The GOPE realizes that Trump is likely to win both the nomination, and in November.
And when he does, he will remember those who tried to cheat him, unless they make peace with him now.
Trump has both the willingness AND the money to ensure well-financed primary campaigns against those he particularly disliked.
You are right, I believe. While much of the opposition is couched in political terms, there are also quite personal reasons the old guard is terrified. Should Trump win, he will have access to data heretofore classified, and many of those secrets are classified merely to protect insiders, not our country. All the buried scandals (Fast and Furious and dozens more) might be finally and completely revealed. People would go to jail. It scares the hell out of them.
The Bushes want a North American Union. That's been their game plan for decades. But Jeb's trash talk is personal. He'll never get over the smackdown Trump administered. Also Jeb is too stupid to understand the Bush family game plan.