Rising Democratic candidate Pete Buttigieg came under attack during a debate among U.S. presidential hopefuls on Thursday, as his rivals questioned the 37-year-old mayor’s thin political resume and criticized his fundraising from wealthy donors.

During the sixth debate for Democrats seeking their party’s nomination to challenge President Donald Trump in the November 2020 election, an intensifying feud between leading contenders Buttigieg and U.S. Senator Elizabeth Warren over transparency and fundraising burst to the surface.

Debating a day after Trump’s impeachment in the Democratic-led House of Representatives, the seven candidates were unanimous in supporting that action, but their unity on the issue quickly gave way to spirited and personal battles over money in politics and experience.

The exchanges underlined the increasing stakes in the Democratic race seven weeks before the first contest in the state-by-state nominating process in Iowa on Feb. 3. Opinion polls show the race up for grabs, with Buttigieg taking the lead in Iowa and former Vice President Joe Biden, U.S. Senator Bernie Sanders and Warren fighting for the top in national polls.

U.S. Senator Amy Klobuchar, lagging the frontrunners and pinning her hopes on a strong showing in Iowa to propel her candidacy, also took a shot at Buttigieg by comparing her Senate accomplishments to his public record.

Warren questioned whether Buttigieg, the mayor of the Indiana city of South Bend who previously served in the U.S. military and was deployed to Afghanistan, was beholden to his big-money donors and described his ritzy, closed-door fundraiser in a wine cave in California. In a shot at Buttigieg, Warren said she did not sell access to her time or “spend time with millionaires or billionaires.”

“The mayor just recently had a fundraiser that was held in a wine cave full of crystals and served a $900-a-bottle wine,” said the Massachusetts senator, who does not hold big-ticket fundraisers and has focused her campaign on fighting corruption and corporate greed.

“Billionaires in wine caves should not pick the president of the United States,” Warren said.

Buttigieg shot back at Warren, who has a net worth in the millions of dollars, noting that he was the only candidate on the stage who was not a millionaire or billionaire.

“This is the problem with issuing purity tests you cannot yourself pass,” Buttigieg told Warren.

“Your net worth is 100 times mine. We need the support from everybody who is committed to helping us beat Donald Trump,” Buttigieg added.

Klobuchar noted Buttigieg’s failure to win statewide election in Indiana.

“Try putting together a coalition to bring you back to office with 80% of the vote as a gay dude in Mike Pence’s Indiana,” Buttigieg said, referring to the U.S. vice president, who previously served as governor of Indiana and is an opponent of gay rights.

The less-crowded debate stage, which featured the fewest participants since the debates began over the summer, gave more time to middle-tier contenders. Klobuchar and entrepreneur Andrew Yang took the spotlight in several of the night’s most memorable moments.

A day after the historic impeachment vote, the candidates promised to make the case to a divided American public that Trump’s impeachment was necessary. They said his leadership had diminished the country’s stature and respect abroad.

“It’s not only in the Middle East we see the consequences of the disappearance of U.S. leadership,” Buttigieg said, noting Trump was ridiculed behind his back at a recent gathering of world leaders. “It’s not just the mockery at a cocktail party. … It’s the looks on the faces.”

The House on Wednesday impeached Trump on charges of abuse of power and obstruction of Congress arising from his request that Ukraine investigate Biden and Biden’s son Hunter, who had joined the board of Ukrainian energy company Burisma while his father was U.S. vice president.

Klobuchar said she wanted to hear testimony from top White House aides at the Republican president’s trial due next month in the Republican-led Senate, which will determine whether Trump is removed from office.

“If President Trump thinks he should not be impeached, he should be not scared to put forward his own witnesses,” Klobuchar said. “The president is not king in America. The law is king.”

The candidates acknowledged that the American public is split over impeachment, with Republicans largely opposing it and Democrats favoring it. But they said it is a fundamental question of right and wrong.

“We have to prosecute the case against him, and that means we need a candidate for president who can draw the sharpest distinction,” said Warren, who will serve as a juror in the Senate trial.

Sanders, another of the jurors, said the United States “cannot have a president with that temperament who is dishonoring the presidency of the United States.”

With deep and widening partisan divisions in the United States, Biden made the case for the importance of Democrats being able to work with Republicans.

“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. If that’s the case, we are dead as a country,” Biden said.

“If anyone has reason to be angry with the Republicans and not want to cooperate it’s me,” Biden added. “They have attacked me and my son and my family. I have no love. But the fact is, we have to be able to get things done.”

In a party that prides itself on its diversity, the debate lineup has been criticized for being nearly all-white – Asian-American Yang was the only minority candidate to qualify.

“It’s both an honor and a disappointment to be the only candidate of color on the stage,” Yang said.