In a vigorous effort to slow Bernie Sanders' momentum in the fight for the Democratic nomination, Joe Biden and Pete Buttigieg argued that Democrats are putting control of the House and Senate in jeopardy.

All of the top Democratic candidates turned their fire on Sanders -- and one another -- in the chaotic opening hour of Tuesday's 10th Democratic presidential primary debate, underscoring the sudden urgency in halting his momentum as desperate candidates face a critical phase.

The former South Bend, Indiana, mayor argued that if Sanders becomes the Democratic nominee it would mean "four more years of Donald Trump, Kevin McCarthy as speaker of the House and the inability to get the Senate in Democratic hands."

"The time has come to stop acting like the presidency is the only office that matters," Buttigieg said. "Not only is this a way to get Donald Trump reelected. We have a House to worry about. We have a Senate to worry about. And this is really important."

"If you want to keep the House in Democratic hands, you might want to check with the people who actually turned the House blue," Buttigieg said to Sanders. "Forty Democrats who are not running on your platform. They are running away from your platform as fast as they possibly can. I want to send those Democrats back to the United States House."

Biden also made a similar argument, noting that many of the Democratic candidates who flipped red districts to blue in 2018 are supporting his campaign.

The former vice president also defended his standing in the black community after the moderator noted that he has been losing ground among black voters in South Carolina.

"I've earned the vote, I've worked like the devil to earn the vote of the African American community, not just here but across the country," Biden said. "I've been coming here for years and years, creating jobs here, making sure that the port, for exampl -- that employs one in 11 people -- we put $500 million in our administration just into this county. We've created jobs for people."

When asked if he would drop out of the race if he does not win in South Carolina, Biden replied: "I will win South Carolina."

Candidates spend debate chirping at one another

The opening hour of the debate, hosted by CBS and the Congressional Black Caucus Institute, 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 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.

Sanders was hammered by all of the candidates on his foreign policy agenda. Moderators opened the topic by asking him whether the American people could trust him to oppose the actions of authoritarian leaders.

"I am not looking forward to a scenario where it comes down to Donald Trump with his nostalgia for the social order of the 1950s and Bernie Sanders with nostalgia for the revolutionary politics of the 1960s," Buttigieg said. He again alluded to the down-ballot House and Senate races.

"We're not going to win these critical House and Senate races if people in those races have to explain why the nominee of the Democratic Party is telling people to look at the bright side of the Castro regime."

Klobuchar sought to pivot to the cost of Sanders' ideas through the lens of his embrace of socialism.

"We have a huge choice," Klobuchar said. "Do you want to have someone in charge of this ticket who wants to put $60 trillion in spending, three times the American economy? I don't think we do. I think we can get all the bold progressive things done without having someone so alienating that we're going to turn off the voters that we need to bring with us."

Sanders responded that his favorability ratings were "among the highest up here" onstage, and went on to describe how he would win.

"We need a campaign of energy and excitement," Sanders said. "We need to have the largest turnout in the history of the United States. We need to bring working people back into the Democratic Party. We need to get young people voting in a way that they never have before. That is what our campaign is about."

Early in the night, 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 then leapt at the moderator's invitation to take on Sanders' ideology as a democratic socialist.

"Vladimir Putin thinks that Donald Trump should be president of the United States," Bloomberg said. "And that's why Russia is helping you get elected, so you will lose to him."

Sanders shot back that Bloomberg is "a good friend of President Xi of China... an authoritarian leader."

"Let me tell Mr. Putin, who interfered in the 2016 election, try to bring Americans against Americans," Sanders said. "Hey, Mr. Putin, if I'm president of the United States, trust me, you're not going to interfere in any more American elections."

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.

Asked why Russia would want to help Sanders' campaign, 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.

Biden looks to go on offense before South Carolina

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.

Biden repeatedly returned to the issue of gun violence as a way to contrast his candidacy with that of Sanders.

"My friend to my right, and others, have, in fact, also given to the gun manufacturers absolute immunity," Biden said. "Imagine if I stood here and said we give immunity to drug companies, we give immunity to tobacco companies. ... I want to tell you if I'm elected, I'm coming for you and gun manufacturers, I'm going to take you on."

When Sanders was asked why he voted to give gun manufacturers a pass, he tried to turn the question on Biden -- to boos -- by noting that the former Delaware senator voted in support of the invasion of Iraq.

"My point was ... I have cast thousands of votes, including bad votes," Sanders said. "That was a bad vote."

He noted that he now has a D-minus rating from the National Rifle Association.

Bloomberg noted his work funding Moms Demand Action, the volunteer wing of Everytown for Gun Safety.

"I have a million person organisation around this country," Bloomberg said. "We've gotten background checks in 20 states, so you can do it. It's Congress that can't seem to do it."

Sanders repeatedly argued that his positions on guns decades ago were not as relevant as his position now.

"Here is the good news, because of all these disgusting mass shootings, the American people now understand that we must be aggressive on gun safety; (we will) not be dictated to by the NRA, and I am proud I have a 'D minus' record from the right. If elected president it will be worse than that," he said.