Pete Buttigieg, whose popularity has surged in recent days, found himself the sudden target of attacks at Wednesday night's fifth Democratic primary debate but sought to stay on the offensive and make an appeal to the country's political middle with a blunt rebuke of Elizabeth Warren and Bernie Sanders' "Medicare-for-all" plan.

He was joined by several other candidates on stage in going after the health care overhaul, putting the party's far-left candidates on their heels over what Buttigieg called their "divisive" and unrealistic approach.

Reflecting the ever-shifting dynamic in the race, meanwhile, Joe Biden had a mixed performance -- projecting foreign policy strength and siding with Buttigieg against the liberal wing on health care, while also suffering some stumbles on the debate stage. Until recently the unrivaled front-runner in the race, Biden competed for attention Wednesday with three other top-tier candidates -- Warren, Sanders and Buttigieg -- but flubbed when he erroneously stated in front of Sen. Kamala Harris that he had the support of the "only" black woman elected to the Senate.

In an odd moment, he also said it's important to "keep punching at" the problem of domestic violence, noting that it's "rarely" needed for men to hit women in self-defense.

The debate was the candidates' first meeting since Warren said she would gradually guide the nation toward Medicare-for-all, supposedly paid for with a host of tax hikes on the rich and other measures. One by one, several of the candidates -- including Biden, Sen. Cory Booker and Sen. Amy Klobuchar -- raised objections to that plan.

"I’m not going to go for things just because they sound good on a bumper sticker and then throw in a free car," Klobuchar said at one point.

Buttigieg called for health care reform "without the divisive step of ordering people onto it," saying that "commanding people to accept that option" is not the right approach.

"We have a majority to do the right thing if we can galvanize, not polarize, that majority," the South Bend mayor said.

And, in a particularly spirited moment, New Jersey Sen. Booker directly took on Warren's proposed wealth tax, saying it would be ineffective as a means of funding her Medicare-for-all plan, along with her proposals to provide free college tuition and erasing student loan debt.

Democrats need to be focused on growing wealth, Booker said, not simply taxing it. Republicans have asserted that, even if all billionaires were somehow taxed out of existence without causing any capital markets distortion, the resulting revenues in the best case scenario would barely pay for three years of Medicare-for-all. (The world's 2,150 billionaires have an approximate combined net worth of $8.7 trillion, and the progressive Urban Institute has said that Medicare-for-all would cost on average $10.2 trillion for three years.)

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Vermont Sen. Sanders, who is arguing for a more immediate shift to a single-payer system, separately sparred with Biden on the issue. Biden argued that Medicare-for-all could not pass Congress, in part because it would force people to lose their private insurance.

"I trust the American people to make a judgment about what is in their interest, and not demand of them what the insurance companies want," Biden said. He continued to push for modifications to Obama-era health care reforms instead.

On foreign policy, Biden sounded an authoritative note, declaring that he would restrict arms sales to Saudi Arabia following the murder of dissident journalist Jamal Khashoggi. “We have to speak loudly on violations of human rights," he said, unequivocally holding Crown Prince Mohammad Bin Salman responsible for Khashoggi's death.

Later, in a somewhat awkward moment, Biden prompted some laughter in the audience when he declared that "we gotta keep punching at" the problem of domestic violence, and that it is only acceptable to hit a woman in "self-defense," which he said would "rarely" occur.

And, Biden asserted that he had the support of "the only African-American woman who’s ever been elected to the United States Senate" -- prompting Booker and Harris to dryly remark, "That's not true."

Harris noted, “The other one is here.” Biden later corrected himself to say he had the support of the first African-American woman elected to the Senate, referring to former Illinois Democratic Sen. Carol Moseley Braun.

In another notable one-on-one moment, Sanders, touting the benefits of socialism in a discussion with billionaire Tom Steyer, argued that America only has "eight or nine" years left to reverse catastrophic effects of climate change, including cities going "underwater." United Nations experts made similar claims all the way back in 1989.

As the heated discussion unfolded at the MSNBC debate in Atlanta, Hawaii Democratic Rep. Tulsi Gabbard -- who was recently accused by Hillary Clinton of being a "Russian asset" -- offered a blunt assessment: "Our Democratic Party, unfortunately, is not the party that is of, by and for the people," she said.

Gabbard also doubled down on earlier comments that Clinton represents the “personification of the rot in the Democratic Party.” She said the party is influenced by a “foreign policy establishment” that supports regime-change wars. She called it the “Bush, Clinton, Trump foreign policy doctrine.” (Harris then attacked Gabbard for appearing on Fox News.)

Separately, Gabbard unloaded on Buttigieg after he attacked her for a widely-panned meeting with Syrian dictator Bashar al-Assad, who is accused of war crimes.

"You would lack the courage to meet with both adversaries and friends," Gabbard shot back, noting that former President John F. Kennedy met with his counterpart in the Soviet Union.

Klobuchar also pointedly criticized Buttigieg, arguing that he "said the right words" as a "local official" but lacks needed experience.

"I actually have the experience," Klobuchar remarked.

"Washington experience is not the only experience that matters," Buttigieg retorted. "There's more than 100 years of Washington experience on this stage, and where are we right now as a country?"

Meanwhile, Warren unloaded on U.S. Ambassador to the European Union Gordon Sondland just hours after his explosive impeachment hearing testimony, saying at Wednesday night's primary debate that he bought his position "by writing a check for $1 million" to Trump's inaugural committee.

Warren vowed that if she were elected, "We are not going to give the ambassador posts to the highest bidder" -- signaling that the Massachusetts Democratic senator would use the proceedings to advance her outsider message.

However, The Washington Free Beacon noted that Warren repeatedly voted to confirm several of former President Barack Obama's donors to ambassadorships, even when they lacked relevant experience. And, Warren did not object to Sonland's confirmation at the time.

"Read the Mueller report, all 442 pages of it, that show how the president tried to obstruct justice," Warren said. "We have to establish the principle that no one is above the law. We have a constitutional responsibility, and we need to meet it."

Others on stage also slammed President Trump over the impeachment proceedings.

“We have a criminal living in the White House,” Harris, D-Calif., declared. Citing Sondland's claim that everyone was "in the loop" on Ukraine talks at the heart of the probe, she said "that means it is a criminal enterprise engaged in by the president" and other top officials.

Not everyone on stage committed to voting to convict the president if he were impeached, however. Klobuchar suggested she wanted Trump removed, but emphasized the importance of seeing all the evidence.

"I have made it very clear that this is impeachable conduct. ... I just believe our jurors is to look at each count and make a decision," Klobuchar said, before saying that Trump repeatedly "puts his own private interests ... in front of our country's interest."

The debate's initial attention on Trump and Medicare-for-all took some heat off Buttigieg, at least for the debate's beginning moments. His dramatic rise from little-known Indiana mayor to a leading Democratic presidential candidate faced its toughest test on Wednesday, with rivals eager to stall his momentum.

Harris and Buttigieg engaged in a tense but respectful conversation later on in the evening, as Harris discussed the importance of not taking "women of color" for granted.

"I do sometimes feel like a stranger in my own country," Buttigieg, who is openly gay, remarked.

The debate in Atlanta marked the first time Buttigieg faced other White House hopefuls as an undisputed member of the top tier.

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The 37-year old mayor of South Bend, Indiana, gained significant ground in recent months in Iowa, which holds the nation’s first caucuses in February. He is bunched at the top of most polls in Iowa with candidates who have much longer political resumes.

Veteran Democratic consultant and communications strategist Lynda Tran said Buttigieg “is on the rise, and that means he should anticipate the other candidates on stage this week to set their sights on his campaign.”

Some surveys are beginning to show him taking a more convincing lead in the race, at least in early-voting states.

Buttigieg still faces plenty of hurdles to clinching the Democratic nomination, particularly winning over black and other minority voters. But his Iowa rise means he could come under fire from his rivals like never before.

Biden, Warren and Sanders have all faced similar scrutiny in previous debates, and those attacks did little to change the trajectory of the race.

The debate unfolded at a moment of uncertainty about the Democratic field, with some in the party, particularly donors, worried there’s no one positioned to defeat President Trump. Former President Barack Obama took the unusual step last week of warning the party against moving too far to the left.

Speaking to that anxiety, former Massachusetts Gov. Deval Patrick entered the Democratic race last week. Billionaire Michael Bloomberg, the former New York City mayor, is openly flirting with a bid.

Neither Patrick nor Bloomberg were onstage Wednesday.

With less than three months before voting, much of the nation’s political attention would typically be focused on the primary. Instead, the focus is on the impeachment inquiry against Trump.

Booker faces especially intense pressure. He’s yet to meet the Democratic National Committee’s polling requirements for the December debate, and his campaign acknowledges that he needs to capitalize on the national spotlight.

The New Jersey senator took an apparent shot at Buttigieg at one point, following the news that his campaign had used a stock photo of a woman in Kenya who apparently had nothing to do with the campaign.

“I want to turn back to the issue of black voters," Booker said. "I have a lifetime of experience with black voters. I’ve been one since I was 18. Nobody on this stage should need a focus group to hear from African-American voters."

In his rousing closing statement Wednesday night, Booker claimed to throw out his prepared remarks to discuss the "debt" that all Americans owed because of the country's racist history.

"It is time to fight, and fight together," Booker said, as the audience applauded.

Gabbard, for her closing remarks, urged Democrats to defeat the "divisiveness of Donald Trump" and "make Dr. King's dream a reality."

In his closing statement, Buttigieg offered an olive branch to "progressives," as well as "moderates" and "a lot of future former Republicans," emphasizing his efforts to win over moderates throughout the contentious evening.

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"I want you to know that everybody is welcome in this movement that we're building," Buttigieg remarked.

After the candidates left the stage, progressive author and Democratic presidential candidate Marianne Williamson -- who didn't qualify for Wednesday's debate -- tweeted simply, "Miss me?

Fox News' Paul Steinhauser and The Associated Press contributed to this report.