There's another sign — if you needed one — that Jeb Bush is sucking wind in the Republican primary: Three top fundraisers from Bush's home base of Florida have left the campaign.

The particulars of the split are up for debate, according to Politico's Alex Isenstadt and Marc Caputo, who broke the news. But regardless of the proximate cause, it's a big deal because it suggests two larger issues for Bush's campaign: He's dug a big hole, and there's concern in his own camp that he won't be able to dig his way out.

It also comes less than three months after Bush shook up his staff and installed Danny Diaz, a veteran Washington operative, as campaign manager.

In the last public national poll, conducted by Quinnipiac, Bush was tied for third place, behind Donald Trump and Ben Carson, at 7 percent. Ironically, fundraising prowess has been Bush's calling card in a campaign that was supposed to blow his rivals out of the water. Even Mitt Romney, who had to fend off a rotating set of ill-fated frontrunners like Newt Gingrich and Herman Cain, enjoyed a pretty steady rise in polling. Not Bush.

The three fundraising aides left after clashing with national campaign staff, Politico reported, and it's not clear whether they will continue to have a role with Bush's Right to Rise Super PAC. But what is clear is this: It's rare for three high-profile staffers to bolt a campaign they see as likely to land the candidate in the White House, and it's equally rare for a winning campaign to shed three high-profile aides.

The exception that proves the rule: Veteran strategist Roger Stone parted ways with Trump this summer. But everyone who watches politics closely is familiar with the panic cycle:

A struggling campaign shakes up its staff, which sends a signal to supporters both that the campaign is in trouble and that the candidate understands that. Staffers fight over who is to blame for flagging performance in polls. One side wins, and the other heads for the exits.

In early February 2008, Hillary Clinton ousted campaign manager Patti Solis Doyle and replaced her with the team of Maggie Williams and Cheryl Mills. There was no similar shake-up on Barack Obama's winning campaign that year. In September 2004, two months before he would lose to George W. Bush, John Kerry brought on several former aides to President Bill Clinton in a shake-up that the Kerry campaign insisted against all evidence was not a shake-up. Bush, on the other hand, had a remarkably stable stable of advisers in his winning campaigns of 2004 and 2000.

The bottom line: The departure of the fundraisers points to much bigger problems in the Bush campaign.