One of the most significant donors in the U.S. to Democratic causes and candidates came under relentless attack Wednesday night during his first appearance on a debate stage as a candidate for the party's presidential nomination.

But on Wednesday, his fellow candidates savaged him more viciously than they have at almost any other point during his campaign, using their opening answers in the first minutes of the debate to hit the billionaire.

The Democratic candidates took turns assailing Bloomberg's record as mayor of the nation's most populous city and especially his support for the stop-and-frisk policy the New York City police department carried out during his tenure, his company's policy of entering into nondisclosure agreements with women who accused Bloomberg of inappropriate comments, and a lack of transparency on his personal finances that echo President Trump's refusal to disclose his tax reforms.

"Most Americans don't see where they fit if they've got to choose between a socialist who thinks that capitalism is the root of all evil and a billionaire who thinks that money ought to be the root of all power," Buttigieg said, referring to Sanders's refusal to join the Democratic Party and Bloomberg's past as a Republican and an independent. "Let's put forward somebody who's actually a Democrat."

Bloomberg at times showed the drawbacks of being a newcomer on the debate stage after his chief rivals had so much more experience answering sharp questions from moderators in eight previous debates. He stumbled over questions dealing with controversies that have been in the news in recent weeks, including whether he would release women from the nondisclosure agreements, whether his apologies for the stop-and-frisk policies had been sufficient, and whether he would release his taxes before most Democratic voters got a chance to cast their ballots.

"Fortunately, I make a lot of money, and we do business all around the world. And we are preparing it," Bloomberg said of releasing his tax returns. "The number of pages will probably be in the thousands of pages. I can't go to TurboTax."

In a cutaway shot, Buttigieg and Klobuchar turned to each other, doubled over in laughter.

"OK, yeah, I'm just looking at my husband in the front row that has to, like, do our taxes all the time. We probably could go to TurboTax," Klobuchar said.

Bloomberg's rise, fueled by his unprecedented spending on television advertisements in states that will vote on Super Tuesday, has put him in a promising position to vault into second place in the race for delegates against Sanders after 14 states, a territory and a group of Democrats living overseas vote. Polls show him in the lead or close to it in Super Tuesday states such as Virginia, Oklahoma and even delegate-rich California.

“You know you are a winner when you are drawing attacks from all the candidates. Everyone came to destroy Mike tonight. It didn’t happen. Everyone wanted him to lose his cool. He didn't do it. He was the grownup in the room,” Bloomberg’s campaign manager Kevin Sheekey said in a post-debate statement.

But for a party that rails against the influence of big money in politics, the notion of nominating one of the 10 richest men in the country is anathema to the candidates who have spent years building grassroots movements of supporters who chip in small-dollar contributions. Sanders, whose yard signs say they are paid for by "not the billionaires," seemed especially outraged by Bloomberg's spending.

"Mike Bloomberg owns more wealth than the bottom 125 million Americans. That's wrong, that's immoral," he said.

Sanders, who has leapt to a significant advantage in national polls of Democratic voters, seemed to be best positioned to take advantage of the Democratic attacks on Bloomberg. In yet another debate, the other candidates spent more time attacking the former New York mayor — or each other — than the candidate who is actually leading. Sanders came under more fire, from candidates like Klobuchar, Buttigieg, Biden and even Warren, his closest ideological ally on stage, than he has in previous debates, but only Buttigieg appeared to see the Vermont senator and Bloomberg as the primary threats.

"We shouldn't have to choose between one candidate who wants to burn this party down and another candidate who wants to buy this party out," Buttigieg said.

The Democratic candidates will meet for a 10th time in South Carolina next week, in a debate that is likely to be equally intense, with so much on the line before Super Tuesday on March 3. In a post-debate interview, Biden said he had offered Bloomberg some words after their first clash.

"I said welcome to the party, man," Biden said on MSNBC.