The first half of the sixth Democratic presidential debate started sleepily, but a blistering exchange over the role of money in politics between Sen. Elizabeth Warren and Mayor Pete Buttigieg laid bare one of the few issues where many of the candidates stand in stark contrast.

Warren and Buttigieg—whose campaigns have been defined, respectively, by Warren’s steadfast refusal to host fundraisers and Buttigieg’s well-tuned fundraising machine—tore into each other over Buttigieg’s willingness to host high-dollar fundraisers with wealthy donors. Warren said it made him susceptible to corruption, and Buttigieg said it was a “purity test” that Warren herself could not pass.

“I made the decision when I decided to run not to do business as usual,” Warren said, detailing the 100,000 selfies she has taken with supporters at rallies. “That’s 100,000 hugs and handshakes and stories, stories of people struggling with student loan debt, stories of people that can’t pay their medical bills, stories from people that can’t find child care.”

Unlike some candidates, Warren continued, who travel from coast to coast “to people who can put up $5,000 or more in order to have a picture taken, in order to have a conversation, and in order, maybe, to be considered to be an ambassador.”

Buttigieg, whose recent appearance at a high-dollar fundraiser held in a lavish Napa Valley wine cave, remarked that he couldn’t help “but feel that might have been directed at me.”

“We’re in the fight of our lives right now,” Buttigieg responded, saying that Trump and his Republican allies wouldn’t hesitate to take every dollar possible to keep the White House, and that to beat him, Democrats couldn’t fight “with one hand tied behind our back.”

Warren responded by detailing Buttigieg’s most recent fundraiser, replete with details about crystal chandeliers and $900 bottles of wine.

“The mayor just recently had a fundraiser that was held in a wine cave full of crystals and served $900-a-bottle wine. Think about who comes to that.” Unlike Buttigieg, Warren said, “we made the decision many years ago that rich people in smoke-filled rooms would not pick the next president of the United States.”

In response, Buttigieg turned around what he called Warren’s “purity test,” accusing her of being unable to pass it herself.

“Senator, your net worth is 100 times mine,” Buttigieg said, noting that Warren herself has held high-dollar fundraisers in the past and has transferred some of that money into her presidential campaign. “This is the problem with issuing purity tests you cannot yourself pass.”

“ The mayor just recently had a fundraiser that was held in a wine cave full of crystals and served $900 a bottle wine. ” — Elizabeth Warren

Warren protested that she, unlike others onstage, does “not sell access to my time.

“I don’t spend time with millionaires and billionaires. I don’t meet behind closed doors with big-dollar donors,” Warren said. “This ought to be an easy step. And here’s the problem: if you can’t stand up and take the steps that are relatively easy, can’t stand up to the wealthy and well-connected when it is relatively easy when you are a candidate, then how can the American people believe you will stand up to the wealthy and well connected when you are president and it is really hard?”

The exchange helped open up an issue-by-issue pile-on targeting Buttigieg on issues from political experience and race relations, an attack that many had predicted in the last debate, after Buttigieg crested at the top of the polls in Iowa and New Hampshire. Warren and Buttigieg—as well as Sen. Amy Klobuchar of Minnesota, who later accused Buttigieg of criticizing her “track record of getting things done”—frequently compete for the same college-educated white voters.