It was perhaps the starkest divide between the front-runners at Thursday’s Democratic debate: the candidates who attend private fundraisers and those who reject them.

On one side are former Vice President Joe Biden and Mayor Pete Buttigieg. They keep their campaigns running, in part, thanks to “bundlers” who organize their colleagues, friends, and family to each contribute up to $2,800, the maximum allowed by law.

If you can “chip in 10 bucks, that's great and if you can drop $1,000 without blinking, that's great, too. We need everybody's help in this fight,” Buttigieg said at the debate in Los Angeles.

On the other side are Senators Elizabeth Warren and Bernie Sanders who have rejected money from wealthy donors, and instead focused on small-dollar donations. “We made the decision many years ago that rich people in smoke-filled rooms would not pick the next president of the United States,” Warren said at the debate.

A flash point was over a recent Buttigieg fundraiser held in a now-infamous Napa Valley “wine cave” owned by a billionaire couple Kathryn and Craig Hall.

A story about the event noted that the Hall wine caves “boast a chandelier with 1,500 Swarovski crystals, an onyx banquet table to reflect its luminescence and bottles of cabernet sauvignon that sell for as much as $900.”

The Halls are an example of the many rich progressive Democrats who are often a key fixture on the campaign trail. According to a profile of the couple, the Halls became wealthy in Texas through a variety of business and real estate ventures. Kathryn once ran for mayor of Dallas and served as the U.S. ambassador to Austria during the Clinton administration. More recently, they have focused on running their winery.

At the debate, Sanders commented on how much time his rivals spend with billionaires like the Halls. “My good friend, Joe, and he is a good friend, he's received contributions from 44 billionaires. Pete, on the other hand, he's trailing, Pete. You only got 39 billionaires contributing,” Sanders said.

How a Buttigieg fundraiser is different from a Biden fundraiser

Both the Buttigieg and Biden campaigns allow a “pool” reporter to cover at least some of these private events and report on who attended and what was said.

Buttigieg’s events are often filled with bold-faced names. He recently raised money from Vogue’s editor-in-chief Anna Wintour in New York and from environmental activist Laurie David in West Hollywood. “I particularly like the way the Mayor describes America’s crisis of belonging in this vexed and vexing time,” Wintour said at her fundraiser.

Buttigieg also reportedly recently raised money from Reed Hastings, the co-founder of Netflix, as well as family members of Google co-founder Sergey Brin, former Google CEO Eric Schmidt, and Facebook COO Sheryl Sandberg. Another event earlier this year was reportedly held at Gwyneth Paltrow’s house.

By contrast, Biden fundraisers still involve plenty of wealthy donors, but with less glamorous backgrounds more fitting for the candidate long known as “Amtrak Joe.”

A recent co-host of a Biden fundraiser in Pittsburgh, for example, was Jim Rooney, the son of the late chairman of the Pittsburgh Steelers. Another co-host of the event was the co-owner of a local diner chain called Pamela's P&G Diner. Buttigieg also held a fundraiser in Pittsburgh this month, but is more likely to raise money in the big-money areas of New York, Los Angeles, and San Francisco.

Lawyers and doctors are a common occupation among Biden fundraiser hosts. In recent weeks, Biden raised money from personal injury lawyers in Las Vegas, from trial lawyers in Chicago, at the home of a maternal-fetal medicine doctor in South Carolina, and from a plastic surgeon in Dallas.

Biden does, indeed, have his elite backers. Billionaire real estate and casino magnate Neil Bluhm co-hosted an event for Biden in Chicago in September saying that Elizabeth Warren and Bernie Sanders “don’t represent the Democratic Party” he supports.

Biden is also often is feted by current and former government officials. A recent swing through the Bay Area featured some tech figures, but also included a fundraiser co-hosted by Richard Blum, the husband of Sen. Dianne Feinstein, who was not present.

There are plenty of areas of overlap. Here’s a fun one: Celebrity chef Danny Meyer and his wife Audrey have, according to pool reports, co-hosted fundraisers for both candidates in December. They raised money for Biden on Dec. 3 and then Buttigieg just eight days later.

‘Fight of our lives’

The case made by both Buttigieg and Biden is that these donors should continue to be included in the process. “We're in the fight of our lives right now,” Buttigieg said Thursday night, adding “this is our only chance to defeat Donald Trump and we shouldn't try to do it with one hand tied behind our back.”

Biden’s answer — after advocating a constitutional amendment to mandate public funding of elections — was that “in the meantime, you’ve got to fund a campaign, and we, in fact, have funded a campaign, average contribution $43.”

Buttigieg pointed out that Elizabeth Warren would certainly fit into a crowd of rich donors. “If I pledge — if I pledge never to be in the company of a progressive Democratic donor, I couldn't be up here. Senator, your net worth is 100 times mine,” he said.

“If you want to donate to me, that's fine,” Warren responded, “but don't come around later expecting to be named ambassador, because that's what goes on in these high-dollar fundraisers.”

The tradition of fundraisers as a campaign stop

Throughout recent presidential campaigns, the position of Warren and Sanders is more of an exception than the rule. Nearly all recent major candidates regularly attended these types of fundraisers.

And they would typically come under attack for participating.

It was at a fundraiser where then-candidate Barack Obama said some voters “cling to guns or religion.” It was also at a fundraiser where Mitt Romney was secretly recorded saying that 47% of voters "are dependent upon government, who believe that they are victims,” and they will vote for then-President Obama “no matter what.”

Buttigieg noted that Warren herself has relied on private, high-dollar fundraisers during her previous runs for office. “Senator, your presidential campaign right now as we speak is funded, in part, by money you transferred, having raised it at those exact same big-ticket fundraisers you now denounce,” he said at the debate. “Did it corrupt you, Senator? Of course not.”

Ben Werschkul is a producer for Yahoo Finance in Washington, DC.

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