“What interest would a Bush PAC have in boosting Cruz?”
I think if Jeb can’t find a poll that would legitimately boost himself, he would want any other candidate than Trump to take SC. They probably figure they can stop Cruz later — after the SEC primary perhaps, but for right now, if the Trump train is not slowed down, he could be nearly impossible to stop.
I think you are probably right.
Remember that Right to Rise is only a Bush SuperPAC as long as Bush is running. And Bush very well could be forced out of the race with Right to Rise still having ten(s) of millions of cash on balance sheet.
When the Right to Rise machers try to figure out what to do, there’s a real chance that supporting Cruz will be the outcome. Rubio is seen as a disloyal, impatient protege of Jeb’s, while Trump of course built his entire campaign in 2015 by disemboweling Bush.