Sen. Elizabeth Warren and Mayor Pete Buttigieg got into a heated battle over high-dollar fundraising in Thursday night’s debate, with Warren slamming the mayor for holding a fundraiser in a Napa Valley wine cave.

Buttigieg countered by accusing Warren of hypocrisy, describing himself as the least wealthy person on the stage and blasting Warren for transferring big-dollar money from her Senate campaign account. The debate brought to the surface a fight that had been brewing between the two campaigns over the last two weeks, as Warren and Buttigieg have challenged each other to be more transparent about their tax returns, private clients, and fundraising.

“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. “Billionaires in wine caves should not pick the next president of the United States.”

Buttigieg accused her of setting up a “purity test” that she herself cannot pass, and said that he would not turn away anyone’s help in the fight to defeat Donald Trump.

“I do not sell access to my time,” Warren said.

“As of when Senator?” Buttigieg asked.

Sen. Bernie Sanders got into the mix as well, noting that he has not received any contributions from billionaires. Sanders said that former vice president Joe Biden had received contributions from 44 billionaires, while Buttigieg was trailing, with contributions from only 39 billionaires.

“So, Pete we look forward to you — I know you’re an energetic guy and a competitive guy — to see if you can take on Joe on this issue,” Sanders said. “This is why three people own more wealth than the bottom half… We need to get money out of politics.”

Sen. Amy Klobuchar also went on offense against Buttigieg, saying he had a thin resume.

“I think winning matters, I think a track record of getting things done matters,” she said.

Buttigieg said he had built a coalition to win re-election with 80% of the vote “as a gay dude in Mike Pence’s Indiana.” Klobuchar shot back that he had lost his only race for statewide office — a campaign for treasurer in 2010 — by 20 points.

The debate — hosted by PBS NewsHour and Politico — had been comparatively sedate in its first hour, touching on issues like China policy and nuclear energy.

Biden struck a conciliatory note in the early going, urging his fellow Democrats to seek cooperation with Republicans, arguing the country will be “dead” if the parties cannot work together. He referred obliquely to President Trump’s efforts to stir up an investigation into Biden’s son.

“I refuse to accept the notion, as some on this stage do, that we can never, never get to a place where we have cooperation again,” Biden said. “If anyone has reason to be angry with the Republicans and not want to cooperate, it’s me — the way they’ve attacked me, my son, my family. I have no love. But the fact is we have to be able to get things done.”

Much of the debate hinged on different visions of how to build a winning coalition against Trump. Buttigieg argued that the tax increases proposed by Warren and Sanders could slow the economy, and criticized their plans to make college free for everyone, saying the richest families should not get a government subsidy.

“We can be smart about the promises we’re making,” Buttigieg said. “On issue after issue, we’ve got to break out of the Washington mindset that measures the bigness of an idea by how many trillions of dollars it can add to the budget, or the boldness of an idea by how many fellow Americans it can antagonize.”

Klobuchar, meanwhile, argued that she is more electable than other candidates because she is from the Midwest.

“The way we tackle this corruption is by winning big in this election,” Klobuchar said.

Later on, Biden was asked about his age, and whether he would pledge to run for a second term if elected.

“No, I’m not willing to commit one way or the other,” Biden said. “I’m not even elected one term yet, and let’s see where we are.”

Tim Alberta, one of the moderators, pointed out to Warren that she, too, would be the oldest president in U.S. history if elected.

“I’d also be the youngest woman ever inaugurated,” she shot back.