Democrats ganged up on former New York City Mayor Michael Bloomberg from the outset of Wednesday night's presidential primary debate, bombarding him with attacks about past controversial policies and comments and comparing him to President Donald Trump.

Each of the other five Democrats on the stage took aim at Bloomberg during their initial remarks but perhaps none as powerfully as Sen. Elizabeth Warren of Massachusetts, who came out swinging by making direct comparisons to Trump's wealth and rhetoric and mentioning allegations against Bloomberg that he's made past sexist and misogynistic remarks.

"I'd like to talk about who we're running against: a billionaire who refers to women as fat broads and horse-faced lesbians – and, no, I'm not talking about Donald Trump. I'm talking about Mayor Bloomberg," Warren said in stinging remarks that induced audible gasps from the debate audience.

With Bloomberg's quick rise in the polls and endless self-funding, Democrats' ninth debate turned into a fast-paced night of confrontations that underscored the wide-open fight for the nomination and highlighted the party's anxiety about fielding a candidate who can beat Trump.

Sen. Bernie Sanders of Vermont, who's considered a front-runner after his narrow victory in New Hampshire and close race in Iowa, was given the first question of the night to explain why he has a better strategy to defeat Trump than Bloomberg, who is making his debate-stage debut in Las Vegas.

Sanders criticized Bloomberg for the controversial stop-and-frisk policy during his time as New York City mayor that disproportionately affected African Americans. Bloomberg has since apologized for the policy but explained that he was trying to curb high murder rates.

"Mr. Bloomberg had policies in New York City of stop and frisk, which went after African American and Latino people in an outrageous way," Sanders said. "That is not a way you're going to grow voter turnout."

Bloomberg, who kept a straight face while several candidates confronted him, including former Vice President Joe Biden and Sen. Amy Klobuchar of Minnesota, rarely engaged and focused on his record as mayor and what he described as his ability to defeat Trump in November.

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"I know how to take on an arrogant con man like Donald Trump that comes from New York. I know how to run a complicated city," he said in responding to Warren's criticisms, adding that he's a philanthropist "who didn't inherit his money" like the president.

But Bloomberg did respond to Sanders, a self-described democratic socialist, arguing that the senator would deliver Trump another four years in the White House.

"I don't think there's any chance of the senator beating Donald Trump," Bloomberg said, adding that his plan of "'Medicare for All' would take away the insurance they love." "And if he goes and is the candidate, we'll have Donald Trump for another four years and we can't stand that."

Wednesday night is Bloomberg's first major test of the 2020 campaign and the first time he's been directly confronted by his opponents. The former mayor, who has an estimated net worth of $60 billion, has already spent hundreds of millions of dollars on national advertising but has skipped campaigning in the four early states.