The Top 3 Things Worrying Jeb Bush Donors

— -- Republican presidential candidate Jeb Bush's wonkish ways may be turning off voters and some donors are starting to worry that their man is not living up to expectations. Here are three issues keeping donors up at night:

Polls

In national polls, Bush has trailed Donald Trump for weeks and is now solidly behind Ben Carson and Carly Fiorina.

"Would I like to see him as the front-runner? Of course!” one major bundler said. Another fundraiser based in New York was impressed with Bush's debate performance but is worried that Bush has lost his footing in the crowded GOP field. The latest NBC/WSJ poll shows that Bush is down 7 points since late July.

The Washington Post reported that some Bush donors may defect if Bush's popularity sags.

Bush senior adviser and fundraiser Austin Barbour discounts any notion that donors could stray.

"I don't think any rational or reasonable person looking at this race is going to go switch horses right now by looking at polls," said Barbour, who is also tasked with campaign fundraising.

Other Bush advisers have stressed to ABC News that the campaign is in its early phases.

"I've been fortunate to deal with donors for over a decade. Donors are always gonna be nervous, you got to love them for it," Barbour added. "Politics to many of them is a foreign sport and they don't understand the ebbs and flows of a campaign. They will be nervous until election day and that's just how it is."

Marco Rubio

Bush supporters have long said the Florida junior senator posed a greater threat than any other candidate.

Al Cardenas, a longtime Bush confidant and well-known Florida Republican, said Rubio was running as the youthful alternative to Bush. Prior to Trump's candidacy Cardenas said he believed "the battle for nomination would be [partially] based on experience versus youth."

Now, perhaps, his prediction is coming true. This week Rubio has seen a surge in the polls, and is ahead of Bush in the latest NBC/WSJ poll.

Bundlers and donors alike recognize Rubio's charm. Others describe him as attractive, articulate, youthful and a more credible challenge than the politically inexperienced Fiorina and Carson.

"He's a really good communicator," Barbour admits. "But voters are going to look for an executive...voters will look at Rubio's experience and it doesn't match up."

Visibility

Even though Bush is maintaining a vigorous campaign schedule, some are worried that his name and his personal record haven't managed to break through with voters. One fundraiser spoke of how impressive she finds Bush in smaller settings and laments that more people haven't seen that side of him. She echoes the sentiments of other advisers who are waiting for the crowded field to thin so that Bush can shine.

Meanwhile, if Bush's campaign staffers are worried, they're not letting it show.

"We're in a really good spot, we want to peak at the right time," Barbour said.

But for all the worries some donors have, Donald Trump is conspicuously absent from this list.

Bush donors said Trump is just a distraction distraction and they're convinced his appeal will eventually fizzle and that Bush will emerge victorious.

"Who could have expected a candidate to surface in our party who's broken every tradition of etiquette expected of a presidential candidate?" Cardenas said. "No one has been as coarse, crude, and rude."

"I think it's very very difficult for someone who's never been elected to office to be the nominee," said Barbour.

Neither Fiorina nor Carson, it's important to note, have political experience.