LAS VEGAS — From the opening bell, Democrats unleashed an aggressive verbal assault on New York billionaire Mike Bloomberg and raised new questions about Bernie Sanders' take-no-prisoners politics in a contentious debate Wednesday night on the Las Vegas strip.

The former New York City mayor was forced to defend his divisive record on race, gender and Wall Street in his debate-stage debut, while Sanders, appearing in his ninth of the 2020 primary season, tried to beat back pointed questions about his health and his ability to defeat President Donald Trump this fall.

In a fight for her political life, Massachusetts Sen. Elizabeth Warren was a leading aggressor early against Bloomberg. She called him "a billionaire who calls people fat broads and horse-faced lesbians."

More than anything, the fiery affair marked a high-stakes coming-out event for Bloomberg, who had, until Wednesday, used his extraordinary wealth to run for president almost completely on his terms, in TV ads. The debate came just three days before Nevada voters decide the third contest of the Democratic Party's turbulent 2020 primary season.

The intense criticism he faced Wednesday threatened to undermine his surprisingly swift rise from nonpartisan megadonor to top-tier contender.

Warren wasn't alone in her willingness to lash out at ultrabillionaire.

Sanders lashed out at Bloomberg's policing policies as New York City mayor that he said targeted "African-American and Latinos in an outrageous way."

And former Vice President Joe Biden charged that Bloomberg's "stop-and-frisk" policy ended up "throwing 5 million black men up against the wall."

Bloomberg defended himself on all counts and took a shot at Sanders' electability: "I don't think there's any chance of the senator beating Donald Trump."

While Bloomberg was the shiny new object Wednesday, the debate also marked a major test for Sanders, a self-described democratic socialist who is emerging as the front-runner in the Democrats' nomination fight, whether his party's establishment likes it or not. A growing group of donors, elected officials and political operatives fear that Sanders' uncompromising progressive politics could be a disaster in the general election against Trump, yet they've struggled to coalesce behind a single moderate alternative.

Former Midwestern Mayor Pete Buttigieg attacked both Bloomberg and Sanders, warning that one threatened to "burn down" the Democratic Party and the other was trying to buy it.

He called them "the two most polarizing figures on this stage."

Bloomberg and Sanders may have been prime targets at the outset, but the stakes were no less dire for the other four candidates on stage.

Longtime establishment favorite Biden, Obama's two-term vice president, desperately needed to breathe new life into his flailing campaign, which entered the night at the bottom of a moderate muddle behind former South Bend, Indiana, Buttigieg and Minnesota Sen. Amy Klobuchar. And after a bad finish last week in New Hampshire, Massachusetts Sen. Warren was fighting just to stay in the conversation.

Each of the Democrats took turns teeing off against Bloomberg, in particular.

He stumbled at the outset when pressed on his record in business and allegations of sexual harassment at his company. Several women alleged they were discriminated against and Bloomberg himself created a culture of sexual harassment.

Both Warren and Biden called on him to release women involved in the lawsuits from non-disclosure agreements.

"We have a very few non-disclosure agreements -- none of them accuse me of doing anything other than maybe they didn't like a joke I told," he said.

"They are being muzzled by you and you could release them from that immediately," Warren charged. "Understand this is not just a question of the mayor's character, this is also a question about electability. We are not going to beat Donald Trump with a man who has...(a) drip, drip, drip of women saying they have been harassed and discriminated against."

Bloomberg also waded into dangerous territory when he declined to say when he'd release his tax returns, declaring "it just takes us a long time."

"Fortunately, I make a lot of money and we do business all over the world," he said, adding that his returns would likely take up thousands of pages. "I can't go to Turbotax!"

The debate was set at the Paris Las Vegas hotel on the heart of the Las Vegas Strip, bringing the political circus alongside the showgirls, slot machines and glitz that Las Vegas is known for. The casino, which sits directly across the Strip from the Bellagio's famous fountains, features a replica Eiffel Tower out front with legs that extend inside into the casino floor.

As Democrats were clustered inside the casino, outside on the Las Vegas Strip, Republicans hired a mobile electronic billboard truck to drive slowly in front of tourists, flashing a message promoting Trump's reelection.

Steve Peoples and Alexandra Jaffe reported from Washington. Associated Press writer Kathleen Ronayne in Sacramento, Calif,, contributed to this report.