Who wins the fight could determine which Republican candidate will have the financial juice to go the distance as the race goes national and grows more expensive with an expanded reliance on television ads -- especially against billionaire Donald Trump.
Bush's donors and backers have not coalesced around one candidate, one ally told CNN. Some in the Midwest may choose to back John Kasich, the Ohio governor who finished second in New Hampshire. Those in Texas may anoint Sen. Ted Cruz. And many of the people personally closest to Bush just need time to mull it over. The candidate hasn't made a choice, either.
Marco Rubio, Bush's former protégé in Florida, may turn out to be the biggest beneficiary, despite some personal animosity between the Bush and Rubio orbits. The Florida senator has strong ties to the GOP donor class and fits the mold of a more moderate candidate compared to Trump and Cruz.
Rubio's campaign already had commitments late Saturday from two major Bush donors from Texas and a second pair from California, according to a source close to the Rubio campaign.
Bobbie Kilberg, a prominent Virginia bundler who had backed Chris Christie before jumping briefly to Bush's national finance team, now says she is supporting Rubio as well.
"He is the one candidate who can coalesce the mainstream of the Republican Party and win in the general election," said Kilberg, who received nine calls or emails on Sunday morning from the Christie and Bush worlds asking for her signal in the Republican field. "You will see an indicative movement to Marco in the next week."
Other candidates are pushing forward as well.
Kasich's aides moved quickly on Saturday evening, creating call sheets of Bush donors well before he chose to drop out, according to a Kasich aide with direct knowledge of the matter.
The Ohio governor also started making calls to Bush donors that evening, and planned to spend most of Sunday courting Bush donors as well, said his senior strategist, John Weaver. The campaign had heard from Bush donors in the days leading up to South Carolina, he added.
Cruz's campaign was arguing that it would inherit much of the Bush fundraising shop, with its deep roots in George H.W. Bush's Houston and George W. Bush's Dallas.
And some major Bush backers on Sunday even reported being contacted by the team representing Trump, who has made self-funding his campaign one of his premier calling cards and mercilessly taunted Bush as "low energy" for the past several months.
One Bush bundler contacted by Trump's team told CNN that he was surprised that Trump's aides had beat Rubio's team to the punch. Another financial supporter of Bush heard from a Trump campaign aide on Sunday morning, laying out the reasons why the billionaire will win the nomination and pointing out areas of agreement between the two men.
But some fundraisers are still processing that the candidate who had once pledged to assemble a "shock and awe" fundraising operation failed to turn any of that support into actual votes.
"I just can't flip a switch and go to the next guy," said Jay Zeidman, a Republican bundler from Houston who is anxious for signals from the Bush family about whom to support. "There are a lot of folks loyal to Jeb and to the family. I just can't imagine them saying, 'I am with Marco'" immediately.
It was right before Christmas 2014 when Bush, who had not been seen as a lock to run for higher office, sent word that he was actively exploring a presidential bid. And as the new year turned, he launched a forceful offensive to secure the loyalty of the Republican Party's most generous patrons -- and it worked.
There was New York Jets owner Woody Johnson, who would serve as his national finance chair. Add in Mel Sembler, the Florida developer who helped Mitt Romney raise loads of cash in 2012. And there was former AIG chairman Hank Greenberg, who threw in $10 million to the Bush super PAC, Right to Rise USA, this fall even as Bush struggled in the polls and donors began to worry.
All told, Bush's super PAC raised nearly $120 million -- including $100 million raised in the first six months of 2015, when Bush chose to delay his campaign so he could formally coordinate with the big money group. And when he did launch in June, his campaign raised $11.4 million in just about two weeks, a staggering clip that would slow dramatically as his campaign faltered.
Bush's prowess would soon be outpaced late in the campaign by rivals who assembled similarly strong financial bases. Campaign finance reports released Saturday showed Cruz with more cash on hand than any other Republican, sitting on $13.6 million as of the beginning of the month. Cruz even received $2,700 donations in January from Ben Carson's former top adviser, Terry Giles, and from his bitter establishment rival in his 2012 primary, former Texas lieutenant governor David Dewhurst.
Trump loaned himself $5 million in January as he continues to largely self-finance his bid. Meanwhile, Kasich and Ben Carson were a few beats behind the rest of the GOP field in the size of their warchests.
And even Rubio, who had won over many of the party's most skilled fundraisers as Bush began to struggle last fall, has yet to turn that into a dominant financial position. He only had $5 million on hand -- and that was before a nasty February ad season that dipped deeply into those reserves.
Now, though, they may be replenished -- eventually. As donors called one another on Sunday to see what their fellow Bush fans were thinking, many were unsure about how to move past their loyalty to the Bush family. For others, the wounds from the nasty Bush-Rubio advertising wars remained too raw for them to hop to the Rubio team quickly.
They just need time, Bush fundraisers say. Or for Bush himself to give them a signal for what to do.
He hasn't, yet.