“Joe Biden is a known quantity and quality to” longtime Democratic donors, said Dick Harpootlian, a former chairman of the South Carolina Democratic Party who raises money for Biden’s campaign. “All of us understand what Donald Trump understands — that Biden is the strongest candidate to beat Donald Trump.”

Harpootlian and other fundraisers have tried to step on the gas and collect more big money donations in recent days, to help the Biden campaign build up funds before the expensive spate of caucuses and primaries begin next year.

“He can’t create, out of thin air, an online fundraising mechanism in six months. And we’re getting to the point now where he can’t do a fundraiser every night,” Harpootlian said, because Biden will need to spend more time campaigning in early caucus and primary states.

POLITICO tracked donations by 1,923 “bundlers” for Obama and Clinton — people who raised at least $100,000, and sometimes millions more, for the Democratic nominees in recent years — using data from the Center for Responsive Politics. Biden’s 114 third-quarter donations from this group led the Democratic field, just as he did in the second quarter. Overall this year, Biden has accrued 344 donors from this group.

Kamala Harris was the third-quarter runner-up among Democratic bundlers, with 86. Cory Booker — who threatened to quit the campaign if he didn’t quickly raise $1.7 million at the end of last month — nabbed 78 donations from past bundlers, while Pete Buttigieg got 75. And Elizabeth Warren, who does not hold in-person fundraisers, is growing her support among the traditional Democratic fundraising crowd: 34 of the Obama and Clinton bundlers contributed to her campaign during the third quarter, which ran from the beginning of July through the end of September.

Though he launched his campaign in late April, Biden similarly triumphed earlier this year with elite fundraisers, according to POLITICO’s analysis. Then, as now, he captured about one in four donations from elite fundraisers, with Harris and Buttigieg also netting significant interest.

Biden advisers told POLITICO the former vice president’s online fundraising has picked up significantly in recent weeks, saying Biden raised more money online during the first half of October than he had during the entire month of September. They attributed the uptick to increased enthusiasm for Biden’s campaign and the campaign’s ongoing investment in building a small-dollar donor program.

“It’s always going to be a mix for us” between high- and low-dollar fundraising, Biden deputy campaign manager Pete Kavanaugh said in an interview. “But we have seen a surge in these small-dollar and online donations and our expectation is that that is going to continue.”

The bundler contributions and connections are helping keep Biden’s campaign afloat, but some of those donors are cringing at the way Biden is running his campaign.

“I don’t think Joe Biden is going to be the nominee,” said one major fundraiser, who said he gave to Biden out of loyalty during the third quarter. “I think there’s a thirst for something down the road taking us towards something bigger and better. That’s not going to be Joe Biden, for whom I have the utmost respect. He is acting his age and showing his age.”

Another fundraiser who donated to Biden in the past three months described the former vice president as having two bases of support among wealthy donors: “People who have genuine affection and admiration” for Biden as a person, but are not sure if he can run a great campaign and are supporting other candidates in the Democratic primary while they watch Biden run, and those who feel great loyalty to the former vice president and plan to “ride the horse all the way.”

Biden’s donors are the wealthiest and most prestigious in the Democratic Party. In the past three months, they have included heavyweights such as multibillionaire John Doerr, chairman of the venture capital firm Kleiner Perkins, and fundraiser Emily Blavatnik, who along with her husband, oil tycoon Len Blavatnik, is worth an estimated $19.1 billion, according to Forbes.

Biden has held four high-dollar fundraisers in the past week in New York, Pennsylvania and Greenwich, Conn. — where he was hosted by Connecticut Gov. Ned Lamont and flanked by former Sen. Chris Dodd, a longtime friend and supporter.

But he is still being outraised by candidates with better small-dollar operations.

Biden raised 31 percent of his contributions from small-dollar donors who gave the campaign $200 or less, about half the rate of small-dollar donations powering the Warren and Sanders campaigns, which forgo big money fundraising and raise money predominantly online. Biden also raised significantly less money in small-dollar increments than Buttigieg. The South Bend, Ind., mayor raises money both online and from in-person events, and drew 45 percent of his $19 million haul from small-dollar donors.

The vice president did not start the year with an army of small-dollar supporters from past elections to tap for cash, Biden allies note. But neither did Buttigieg. And all of the candidates started their campaigns needing to reconnect with supporters and refresh their valued email lists, which they use to tap supporters for donations.

Though big-money donors are not enough to carry a campaign, they help juice the funding of several of Biden’s competitors, including Harris, Buttigieg and Booker. Many donors are still willing to give their money to more than one candidate, even within weeks of each other: one in every four fundraisers who gave a donation gave to more than one candidate during the third quarter.

And Warren, who received 39 donations from the fundraisers during her first six months is the race, doubled that number during the most recent quarter, a reflection of quiet, but newly piqued, interest in her candidacy among high-profile donors despite her frequent repudiations of big businesses and traditional political fundraising.

“It doesn’t bother me at all” that Warren is not holding fundraisers, said Philadelphia megadonor Mel Heifetz, who said he agrees with Warren’s politics and would like to see a woman in the White House.

Heifetz — one of the more than 100 fundraisers who gave to multiple candidates in recent months — donated in the third quarter to Warren, Booker and Julián Castro. And this week he attended two fundraisers for his ideal candidate, Buttigieg, who he wishes had a super PAC so that he could pour even more money into his campaign.

“I can afford to give out a lot more hundred dollar bills and have it amount to not so much that I’m worried about it,” Heifetz said.

James Arkin, Scott Bland, Rishika Dugyala, Zach Montellaro, Ally Mutnick, Daniel Strauss and Steven Shepard contributed to this report.