Bush, one former adviser to his father said, “needs to show he’s the tough-minded guy we know he is.” If he doesn’t, the former aide added, “Well, you know, it might be over.”

The Bush campaign privately thinks Bush’s slow-burning fuse – evidenced on the golf course and in sometimes-testy debate sessions – has at long last been lit. But the biggest fear, expressed by Bush allies, donors and party operatives to POLITICO, is that another lousy debate performance will precipitate an exodus of the big money ($100 million-plus in super PAC and campaign cash so far) that has kept the former Florida governor afloat despite his dismal poll numbers.

“The most important thing that Jeb Bush can do right now is to project strength,” says Eric Fehrnstrom, Mitt Romney’s senior adviser in 2012. “Trump’s attacks on Bush as a low-energy candidate have taken their toll. For starters, Bush needs to stop referring to him as “Mr. Trump.” That sounds like he works for him.”