Park City, Utah (CNN) Republican fund-raisers are beginning to fret that Donald Trump does not comprehend the magnitude of the challenge before him, warning that if he fails to execute the basic tasks of fund-raising during a critical six-week stretch, he will find himself badly outgunned this fall.

Over barbeque dinners and en-suite receptions on the grounds of this five-star retreat nestled in the Wasatch Mountains, associates of Mitt Romney's $1 billion presidential campaign swapped concerns with one another that Trump is failing to play catch-up quickly enough. There is hope that Trump can reverse fortunes with a fund-raising swing that began this week, but Republicans worry that he is poised to squander the weeks leading up to the GOP convention.

Obvious bundlers haven't even been contacted. A small-dollar operation is nonexistent. And the fund-raising agreement with the Republican National Committee continues to wobble.

"The fund-raising intensity is missing -- totally," said John Rakolta Jr., a former national finance chair for Romney who said he is flabbergasted to not have received a single phone call from Trump's team. "Who is driving the bus?"

Republicans here stress that the alarm bells have not yet rung: Trump still has five months to assemble a finance team, and several here said they could see themselves coming to his aid if he displayed more maturity as a candidate and tamped down his controversial rhetoric. And given Trump's command of media, more bullish fund-raisers predict that he could survive even a $500 million fund-raising gap against Hillary Clinton's experienced operation.

Spencer Zwick, the much-praised Republican finance operative who led Romney's efforts, said raising $500 million was doable. But Zwick, like several other Republican fund-raisers here, asserted that Trump needed to significantly quicken his fund-raising clip before the convention, after which he will have little time for fund-raising.

And in advance of an event in his hometown of Boston on Monday, Zwick, like Rakolta, said he had received zero contact about it.

"You've got to have an army of people who are out there working for you, and I don't know that they do yet," said Zwick, recalling how Romney raised $100 million in this month four years ago. "I don't know how much Donald Trump wants to spend time raising money."

RNC frustrated

Yet the contrast with the Romney fund-raising juggernaut was on jarring display at the Education and Enthusiasts ideas conference here this week, as Romney's vast orbit of business partners, friends from the 2002 Winter Olympics and political allies roamed the lodge. The refrain, echoed again and again in hushed conversations on the sidelines: Romney built this over decades. Trump has half a year.

And his campaign does not seem urgent, although he would need to raise more than $80 million a month to meet the $500 million mark. After missing out on the windfall of low-dollar cash that could've come Trump's way after each of his primary victories, his campaign is not set to launch a low-dollar digital fund-raising operation until around the Republican convention in mid-July, according to a person with knowledge of the plan.

Trump's campaign didn't respond to a request for comment for this story Friday afternoon. But Trump's national finance chairman, Steven Mnuchin, told CNN's Erin Burnett on "OutFront" in an interview that aired Friday that the majority of the funds will come in during "the latter half of the summer."

"You have to understand we literally just started this in the last four weeks," said Mnuchin, who didn't disclose the amount of money that the campaign has raised so far.

Meanwhile, the Trump high-dollar fund-raising operation is showing signs of duress, people here say. A joint fund-raising agreement was hatched last month to split proceeds between the RNC and the Trump campaign. And while the first joint fund-raisers have gone well, RNC chair Reince Priebus has phoned some associates expressing frustration that Trump wants to direct dollars to his own ambitious plans, according to a person who has spoken directly with Priebus, which includes quixotic bids to win deep blue states like California and New York.

The RNC did not respond to a request for comment.

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Fund-raising invitations in upcoming cities feature few, if any, local supporters. And even some of those listed by the RNC as top-level national backers have signaled that they are not actively raising money for it. Hushang Ansary, a Houston businessman named to the RNC's Presidential Trust team, said he had contributed to the fund but had not picked up the phone to call anyone in his network.

"I wasn't asked to," Ansary said in a phone interview. "I've hardly ever done fund-raising, but I've lent my name to fund-raising efforts from time to time."

And another problem for Trump fund-raising: The Republicans who did it best indicated this weekend largely signaled an unwillingness to pitch in. When pollster Frank Luntz asked a crowd to raise their hands if they would vote for Trump in November, only about 20% of the Romney associates raised their hands, according to Al Cardenas, a prominent GOP lobbyist and fund-raiser.

"The party, frankly, is in a hole. And it needs to figure out how to get folks like us in the room," Cardenas said.

The anti-Trump antipathy was at times intense. Meg Whitman, questioning House Speaker Paul Ryan at a Friday afternoon session, compared Trump to historical demagogues such as Adolf Hitler and Benito Mussolini, according to two sources in the room. A spokesman for Whitman didn't immediately respond to CNN's request for comment.

Despite Trump's toxicity in Romney's circles, very few attendees raised their hands for the Libertarian candidate, Gary Johnson, a former Republican governor. One attendee did indicate an openness to supporting Johnson -- Romney himself, who said he wants to "get to know Gary Johnson better" and expressed an admiration for Johnson's running mate, Bill Weld, in an interview with CNN's Wolf Blitzer.

But almost no attendees said in interviews that they would consider funding Johnson's campaign, which almost certainly would need a major cash infusion to be a credible alternative.

Trump stumpers, though, were trying their best to change those numbers: Anthony Scaramucci, one of the most high-profile Trump fund-raisers, was making the rounds, and Priebus himself came to pitch the RNC to the well-heeled in Deer Valley. Several other prominent Trump supporters, from millionaire restauranteur Andy Puzder to possible Trump running mate Sen. Bob Corker, R-Tennessee, were also spotted.

Trump will win "with or without your help," Priebus told attendees on Saturday morning, according to a person in the room

Romney 'distraught'

But the ultimate signal is being sent by the man himself: Romney, who has emerged as the preeminent leader of the #NeverTrump movement, and has been described by some as "distraught." But the former governor appeared in good spirits as he greeted early arrivals around the torch-lit drop-off lot, led morning expeditions up the mountains as part of an "enthusiast session," and ribbed the older, wealthier crowd as he kicked off one morning event: "Not many selfie voters here."

Yet even as tech titans and authors pitched their big ideas, Trump talk overshadowed everything on the sidelines, where attendees dished about whether he could micro-target effectively and his difficulty recruiting top-flight staff to his team. Others in Romney's orbit were just plain curious. At one Friday session centered on the thinking of millenials, organizers only allowed time for a single question: Is what they say about Trump true?

"They say he's going to bring out 10 to 15 million voters who never vote. Secondly, that he's going to capture 20 to 30% of the (Bernie) Sanders vote," a man asked as hundreds of attendees scrunched in seats between symmetrical paintings of snow-capped mountains. "What do you think about that?"

Many of the attendees here have known Romney for decades and were among his first supporters. And several expressed alarm that Trump had yet to activate his own, similar network of wealthy loyalists that he knows personally, from real estate friend to Manhattan socialites.

"That happens in the primary. I don't think that's happened for Donald Trump," Zwick said, noting that many people on Trump's finance team lack longterm loyalty to his campaign. "Yes, he knows a lot of wealthy people. But where are his friends that are turning out for him and running through walls?"

Romney's network was assembled with people like Randy Boyd, an aide to the governor of Tennessee who was not a longtime bundler but fundraised out of loyalty to Romney.

"He is somebody I would aspire to be like," Boyd said of Romney and who isn't raising for Trump. "The idea of putting my name on anything is anathema to me."