Democratic presidential candidates fanned out on a quest for votes Thursday following a bruising debate that saw billionaire Michael Bloomberg take a pummeling from his rivals.

As the race to see who faces President Donald Trump goes national with 16 states set to vote over the next two weeks, the party battle has taken on fresh urgency, with leftist firebrand Bernie Sanders seeking to cement his status as frontrunner.

Michael Bloomberg
In this file photo taken on February 4, 2020 Democratic presidential candidate and former New York Mayor Michael Bloomberg speaks at a campaign stop in Detroit, Michigan. Photo: AFP / JEFF KOWALSKY

Efforts by rivals to knock Sanders off his perch and blunt a suddenly prominent Bloomberg were reflected in the crossfire in the ninth and most combative debate of the 2020 cycle.

"Worst debate performance in history!" crowed Trump of the former New York mayor's debut presidential debate, which came shortly before Nevada votes on Saturday.

Bloomberg, who has surged in the polls behind hundreds of millions of dollars of spending on television, radio and online ads, was the target of unrelenting attacks all night from the other five candidates on the Las Vegas stage.

Bernie Sanders
Democratic presidential candidate Bernie Sanders addresses supporters during a campaign rally in Denver on February 16. Photo: AFP / Jason Connolly

Massachusetts Senator Elizabeth Warren, who is battling Sanders for the party's left flank, delivered some of the most piercing barbs at the 78-year-old media magnate as she seeks to revive her sagging campaign.

"I'd like to talk about who we're running against: a billionaire who calls women fat broads and horse-faced lesbians," Warren said just minutes into the debate.

"And no, I'm not talking about Donald Trump, I'm talking about mayor Bloomberg," she said, knocking him for delaying release of his tax returns, "harassing women" and supporting "racist policies" like stop-and-frisk crime prevention efforts.

US Elections 2020
View of the Paris Las Vegas hotel which is the venue for Wednesday's Democratic presidential debate. Photo: AFP / Mark RALSTON

If Bloomberg was hoping few Americans would notice the attacks, he was disappointed. The showdown on NBC was the most watched Democratic debate ever, drawing nearly 20 million viewers, the network said, citing ratings analyst Nielsen.

Warren redoubled her fusillade Thursday in North Las Vegas, where she made repeated references to Bloomberg attempting to "buy" the election.

"I have really had it with billionaires, regardless of party, who think that the rules don't apply to them," she told an energised crowd.

Elizabeth Warren
Democratic presidential hopeful Elizabeth Warren, shown here passing out treats to protesting workers in Las Vegas, was under pressure to deliver a command performance in the Democratic debate on February 19, 2020. Photo: AFP / Mark RALSTON

Sanders, the senator from Vermont who has been topping national polls, lashed out at Bloomberg's vast fortune at a time of "grotesque" income inequality in America.

"Mike Bloomberg owns more wealth than the bottom 125 million Americans," the 78-year-old self-described democratic socialist said. "That's immoral."

Bloomberg appeared to be rocked by the ferocity of the attacks and often found himself on the defensive.

US President Donald Trump
US President Donald Trump delivers remarks at a Keep America Great rally in Phoenix, Arizona, on February 19, the same day Democratic White House hopefuls held a contentious debate in Las Vegas. Photo: AFP / JIM WATSON

The three-term New York mayor recovered somewhat as he highlighted his roles as problem solver, successful businessman, city manager and philanthropist who, unlike Trump, grew up in a working-class family and became a self-made tycoon.

But overall it was a shaky performance for a candidate who chose to unconventionally skip the first four nominating contests and make a splash on "Super Tuesday" on March 3, when 14 states including California and Texas hold primaries.

Bloomberg headed to one of those states, Utah, on Thursday for a campaign event where he warned that the debate's "real winner" was Trump because Democrats like Sanders were pushing leftward policies rather than building a broad coalition.

"If we choose a candidate who appeals to a small base, like Senator Sanders, it will be a fatal error," Bloomberg said.

Centrist Senator Amy Klobuchar, who is polling in sixth nationally and faces a make-or-break week, stumped in Colorado, while Sanders was headed to delegate-rich California, where he holds a significant lead.

David Axelrod, who served as chief strategist for Barack Obama's two presidential campaigns, said Bloomberg's "debate implosion" was good news for Sanders although Warren's strong performance keeps her challenge alive.

Sanders and Pete Buttigieg, the former mayor of South Bend, Indiana, will be hoping to build in Nevada and South Carolina on their strong performances in Iowa and New Hampshire.

Former vice president Joe Biden will be looking to rebound from his dismal showing in the first two voting states.

He and Buttigieg both took shots Wednesday at Sanders and Bloomberg.

But while Biden, who has seen Bloomberg cut into his support among moderate Democrats, criticized Sanders over immigration policy and gun reform, it was 38-year-old Buttigieg, with his skillful oratory, who landed the sharper blows.

"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 of Sanders and Bloomberg.

A Washington Post-ABC News poll out Wednesday showed Sanders with a commanding double-digit lead nationally, at 32 percent.

Former frontrunner Biden was second at 16 percent, followed by Bloomberg at 14 percent, Warren at 12 and Buttigieg at eight.

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