(CNN) From the moment Jeb Bush entered the presidential race, his financial backers said they chose him because he was the candidate who could go the distance. But few expected the marathon would be so difficult.

The former Florida governor is fifth in New Hampshire—where he has campaigned hard with a presence on the airwaves. He is trailing Marco Rubio in a new national USA Today/Suffolk University poll and is competing with his one-time understudy for the many undecided donors who are waiting to see how the field shakes out. And Bush is still being overshadowed by the juggernaut that is Donald Trump—as the real estate magnate continues to dominate media coverage that has helped solidify his wide lead in the polls.

In interviews with more than a dozen Bush donors and bundlers this week, many said they are willing to be patient -- for now. But some donors are acknowledging frustration that all of Bush's advantages -- including hard dollars and a capable team with a presence in the four early vote states -- aren't making him a more forceful presence in the race.

"It's as if we keep investing in a company and, as a shareholder, we're not seeing any sales," one Bush donor told CNN, asking not to be named because of the sensitivity of internal campaign discussions.

Other Bush backers -- particularly those who closely watched his steady rise in Florida -- say the team is still hitting fundraising targets while building an aggressive ground game that will give him the resources to reach voters when it counts in the four to six weeks before voters begin casting ballots next February.

"Most of the bundlers and donors supporting Bush are pretty sophisticated—this isn't their first rodeo," said former Florida House Speaker Will Weatherford, a key player on Bush's finance team who made calls to Iowa and New Hampshire this week to lock down former supporters of Scott Walker and Rick Perry.

They know, he said, that "this is the crazy season" -- the point during the campaign in 2011 when Herman Cain and Michele Bachmann topped the polls. "To try to claim that the polls have any relevance right now is just a fantasy. I know it's a good story to write about, but it's just not true, and the bundlers and donors who are smart know that, and have been through enough of these races to recognize it."

"People know that he's built for the long haul and that we're not going to win this thing in October; we're going to win this thing in February and March," Weatherford said.

Of course, outsider candidates -- especially Trump -- are proving to have more staying power this cycle than when Cain and Bachmann were leading the GOP primary.

And there is a recognition that Bush must do more to show he understands and can channel the anger that is drawing Republicans to Trump, Carly Fiorina and Ben Carson.

That is a key element to winning the invisible primary for dollars that is going on behind the scenes—most importantly preventing defections to Rubio. While Bush has lost 50% of his support in the polls since July, the Florida senator poses an increasingly viable threat as he continues on an upward trajectory after his well-received debate performances.

Tellingly, Bush made a pointed contrast with his younger rival in his interview with CNN on Wednesday—going so far as to implicitly compare Rubio with Barack Obama, who was also a first-term senator when he first ran for President.

'Proven leader'

"I'm a proven leader," Bush said when asked why undecided voters should choose him over Rubio, who has cast himself as part of a new generation of leaders better equipped to take on Hillary Clinton. "I disrupted the old order in Tallahassee. I relied on people like Marco Rubio and many others to follow my leadership."

"We moved the needle, led the nation in job growth, reduced the role of government, reformed the things that were broken, took on some very powerful interests, and we won. And I can be that disruptor in Washington, D.C."

"Look," he added, "We've had a president who came in and said the same kind of thing -- new and improved, hope and change -- and he didn't have the leadership skills to fix things."

Party strategists watching from the sidelines say Bush continues to face significant hurdles.

Endurance is important, but so is excitement—and Bush has yet to show that he can create the kind of electricity that would pave the way to the nomination. At campaign events, voters often list him among their top candidates in interviews, but they more often leave impressed, rather than excited.

New Hampshire voter Holly Horner came to see Bush at his town hall meeting in Bedford this week because she wasn't sure he was dynamic enough. She left saying she was "impressed."

"I haven't made up my mind, but I thought he was very rational and he made some good points," Horner said. "He is better in these smaller venues. He gets lost in a big debate."

'Different in person'

Denis Cronin, another Bedford attendee, came into the event unsure of his choice and left more excited after seeing him in person.

"He looks different in person than he comes across on TV. He's very vigorous and very articulate," Cornin said. "He really knows what he's talking about on all of the issues. I was really impressed by that."

Bush faces a stubborn sector of the GOP electorate who say they will not vote for him because of his positions on immigration and Common Core—or because they do not want to see a third Bush in the White House.

"The base of the conservative Republican Party has a great field to chose from. Bush has not been able to excite them," said David McIntosh of the Club for Growth.

Prominent Bush backers and members of his finance team say Bush will wear well on voters over time. A few have suggested tweaks: encouraging Bush get a new pair of eyeglasses, for example.

Many of them urged the candidate to show more dynamism in the last debate—and he did. But there is clearly disagreement among donors about whether he has much to gain by continuing to punch back at Trump.

As Trump has turned his sights to Rubio, Bush has become more dismissive of the real estate magnate, essentially shrugging off his presence in the race. The contest, he told CNN this week, "is not an entertainment."

"We're not auditioning for some kind of show here," he said. "We're running for President of the United States."

Donors say they expect a strong showing this quarter and are pleased by Bush's energy on the trail.

'Getting better'

"Every day that goes by, he's getting better at what he does. It's like riding a bicycle, it comes back," said Gordon Sondlund, one of Bush's key bundlers on the West Coast who helped organize four recent finance events in Seattle and Portland. "The very first few events he might have been a bit rusty, but he's improved exponentially at each event."

He dismissed the suggestion that there is "donor panic" -- largely because Bush's financial backers remain confident in the team even if it has been difficult for his message to pierce through.

"Every time I get down into the weeds (with the campaign), I'm impressed by how much breadth and depth there is to the organization," said Sondlund, who described recent finance events as "well-attended" and noted that he is on the phone daily with fellow donors who are well apprised of campaign strategy.

"I think everyone has their head down and they're focused on the goal, and we haven't seen or heard anything to dissuade us at this point," Sondlund said.

Donors have been frequently invited to headquarters and kept in the loop about the campaign's plans. Former Ambassador Mel Sembler, for example, noted that he sat in and watched as Bush engaged in an intensive policy debate with key Jewish donors last week in Miami.

The campaign has also enlisted donors to press Bush's case with potential endorsers after Walker and Perry's exits from the race. After a series of unflattering stories, the campaign has released an almost daily list of pickups to reporters to drive that point home. One important get was GOP bundler Anthony Scaramucci, who had been raising money for Walker.

Henry Barbour, a Republican strategist who was supporting the former Texas Governor and is now neutral, said it wasn't clear yet whether "anybody is doing any better than anyone else in the Walker-Perry sweepstakes."

At the same time, he said, while "It's best to be someone's first choice, in a race like this, it's really important to be well liked as someone's second or third choice. That could work out well for you come February or March. "

For his part, Bush says he is content to play the long game. At first he called himself the "slow and steady" contender, then the "joyful tortoise" in the race, and now a triathlon competitor.

"I think people want authenticity," he said. "They want someone who has the leadership skills to turn ideas into reality," he said.

As for his current place in the triathlon? "We're swimming," he told CNN this week.