(CNN) -- All of the top Democratic candidates turned their fire on Vermont Sen. Bernie Sanders -- and one another -- in the chaotic opening hour of Wednesday's 10th Democratic presidential primary debate, underscoring the sudden urgency in halting his momentum as desperate candidates face a critical phase.
Sanders managed a quick opening shot at former New York Mayor Michael Bloomberg, targeting his wealth, when asked to explain how he would campaign against Trump when the economy is doing so well.
"You're right the economy is doing really great for people like Mr. Bloomberg and other billionaires," Sanders said to laughter. But after that moment, he was continually on defense.
Bloomberg immediately turned on Sanders, arguing that "Russia is helping you get elected."
Massachusetts Sen. Elizabeth Warren jumped into the conversation by taking a rare shot at Sanders, her longtime ally.
"Bernie and I agree on a lot of things, but I think I would make a better president than Bernie," she said. "The reason for that is that getting a progressive agenda enacted is going to really, really hard, and it's going to take someone who digs into the details to make it happen."
She noted that when she had outlined a more detailed explanation of how she would pay for "Medicare for All," "Bernie's team trashed me for it."
"No," Sanders responded, standing next to her and shaking his head.
The opening hour of the debate was a chaotic affair with candidates shouting over each other as they tried to tear down one another's records. Minnesota Sen. Amy Klobuchar interjected at one point, in a half-hearted plea for party unity before critiquing his record.
"If we spend the next 10 months tearing our party apart, Donald Trump is going to spend the next four years tearing this country apart," Klobuchar said.
But, the candidates spent much of the opening phases of the debate talking over each other and getting increasingly heated as they tried to make a final impression before South Carolina's Saturday primary and next week's Super Tuesday contests. And many of those attacks focused on Sanders.
Asked why Russia would want to help Sanders' campaign, former South Bend, Indiana, Mayor Pete Buttigieg said Russian leaders wanted to sow chaos.
"They want chaos and chaos is what's coming our way," Buttigieg said. He described the past three years under Trump as "chaotic, divisive, toxic and exhausting."
"Imagine spending the better part of 2020 with Bernie Sanders versus Donald Trump," Buttigieg said.
Sanders was always likely to be the main target on Tuesday, rather than Bloomberg, who is not participating in Saturday's contest in South Carolina because he decided to skip the first four primary and caucus states.
With the exception of Buttigieg, the 2020 Democratic contenders have generally handled Sanders with a light touch in prior debates. Former Vice President Joe Biden and Sanders have clashed over "Medicare for All," and Biden and the other candidates have increasingly faulted Sanders for not outlining exactly how he would pay for some of his pricier proposals. Sanders has said he would pay for his plans, in part, through a tax on Wall Street speculation.
But if Sanders pulls off a sizable delegate haul in Tuesday's contests, it could become theoretically impossible for other candidates to catch up to his delegate count, with 1,991 delegates needed to clinch the Democratic nomination.
After his first strong showing in Iowa and his wins in New Hampshire and Nevada, several polls have showed Sanders encroaching on Biden's once-dominant lead among black voters. The former vice president targeted Sanders' record on guns, faulting him for voting against the Brady Bill in 1993. He noted that he had advocated for a longer waiting period in the bill before a person could make a handgun purchase, and that Sanders had opposed that. Biden then invoked the 2015 massacre at Mother Emanuel AME Church in Charleston.
"I'm not saying he's responsible for the nine deaths, but that man would not have been able to get that weapon had the waiting period been what I suggested," he said.
"Bernie in fact hasn't passed much of anything," Biden said at one point about Sanders' legislative record.
Other candidates look for major moment
Biden's campaign also put out a digital ad this week taking Sanders to task for stating in 2011 that it would be a "good idea" if then-President Barack Obama faced some "primary opposition" in his quest for reelection.
Bloomberg, who has spent more than $450 million on television ads in the states beyond South Carolina, has also targeted Sanders as a socialist whose views are out of step with mainstream America. He is expected to highlight his disagreements with Sanders on gun issues, which was the focus of a new ad he released this week.
Like other Bloomberg advisers, O'Brien predicted that his own candidate has now gained his "sea legs" and would be better prepared for any attacks that come his way tonight.
"I think he has to be ready to be the target of everyone else on stage," O'Brien said. "There was something of a circular firing squad in the last debate. I think he got his sea legs halfway through that debate, but he has to have his sea legs at the beginning of the debate tonight for sure."
Biden is fighting for survival, counting on the support of black voters who dominate the primary in the Palmetto State to carry him to victory in a place that he once called his firewall.
Buttigieg, Warren and Minnesota Sen. Amy Klobuchar are all hoping for breakout moments that would lend an air of viability -- and an infusion of cash -- to their campaigns as they head into Tuesday's blockbuster primary, where 14 states and one territory will award a total of 1,357 delegates.
Warren's impressive performance in the Las Vegas debate, where she took Bloomberg to task for sexual harassment and gender discrimination lawsuits against himself and his company, gave a much-needed jolt of energy to her campaign. The Massachusetts senator raised $9 million over three days, according to her campaign manager, granting her a reprieve at a time when federal campaign finance reports show she was running out of money.
Bloomberg last week did offer to release three women from their nondisclosure agreements, if they contacted his company.
This is a breaking story and will be updated.
