“Marco is so much better communicating and makes the generational point without saying a word,” said one big contributor supporting Bush. “Basically the fear is really about Rubio gaining traction with donors. With money, he is the real problem for Jeb.”

The 2016 primary contest could resemble the fracas in 2012, when super PAC benefactors kept alive the bids of former House speaker Newt Gingrich and former U.S. senator Rick Santorum of Pennsylvania, forcing Mitt Romney into an extended fight for the nomination.

Adelson and his family poured $15 million into a super PAC backing Gingrich, then an unthinkably large amount. This time, with more big spenders in the mix, such sums could be commonplace, the former House speaker said.

“What seems like really big money is less than a yacht,” Gingrich said in an interview. Wealthy donors could decide that “this year, instead of buying a new yacht, I’m going to spend $70 million on a candidate,” he said.