In the most contentious Democratic debate thus far, a winnowed field of 10 Democratic candidates took the stage in Houston Thursday night and sparred over hot-button issues such as health care and immigration.

Notably, this was the first time that frontrunners Sen. Elizabeth Warren and former Vice President Joe Biden shared the debate stage. At the end of the night, Joe Biden emerged as the winner and Warren and Sen. Bernie Sanders were the surprise losers.

Warren and Biden exhibited stark differences on style, policy and vision for the Democratic Party, embodying two opposing theories of what the party should be.

DEBATE DESCENDS INTO MELEE OVER HEALTH CARE, OBAMA, SOCIALISM AS DEMS STRUGGLE TO SHOW UNITY

This divide was apparent during an explosive debate over health care, during which Biden went on the attack against Warren, D-Mass., and Sen. Bernie Sanders, I-Vt., for the hidden costs associated with their “Medicare-for-all plans.”

Warren deflected when asked if middle-class taxes will go up to pay for “Medicare for all,” saying total costs would go down – but not explicitly stating whether taxes for middle-class families would increase.

“What we're talking about here is what's going to happen in families' pockets,” Warren said.

“This is about candor, honesty,” Biden retorted. “There will be a deductible – in your paycheck ... someone making 60 grand with three kids, they're going to end up paying $5,000 more.”

SURPRISING LOSER: ELIZABETH WARREN

Though many were watching Warren expecting her to deliver a knockout performance, the senator fell somewhat short of that expectation. While this will likely not impact Warren’s standing in the presidential race at this early stage – which according to most polls is a close second behind Biden – she did not have the debate moment that many were anticipating. She was a surprise loser when the evening was over.

Aside from Biden’s generally strong performance, he compellingly and convincingly delivered his core message of restoring, protecting and rebuilding the Obama-Biden record.

WINNER: JOE BIDEN

On the other hand, the first 30 minutes of the debate during the health care discussion were arguably Biden’s best moments on the campaign trail to date. Though the former vice president’s performance was not perfect, he exhibited a much-needed display of strength and preparedness. He was the night's big winner.

Aside from Biden’s generally strong performance, he compellingly and convincingly delivered his core message of restoring, protecting and rebuilding the Obama-Biden record.

“The senator says she's for Bernie. Well, I'm for Barack,” Biden said about Warren's support for “Medicare-for-all,” referencing last month’s debate, when Warren said she completely agreed with Sanders on “Medicare-for-all.”

At the previous debate, several progressive candidates took aim at former President Obama’s legacy on health care as a way to attack Biden on his record.

However, in a marked reversal, both Warren and Sen. Kamala Harris of California – who sharply criticized Obama in the last debate – praised the former president for the positive systematic changes to health care that came as a result of ObamaCare.

Indeed, if there was an absentee winner of the debate, it was Obama. Aside from Biden, one of the clearest, and most concise health care arguments came from Sen. Amy Klobuchar of Minnesota, who has polled consistently in the low single-digits and had yet to have a strong debate moment before Thursday night.

Klobuchar said that although Sanders may have written the “Medicare-for-all” bill, she “actually read the bill,” noting that under Sanders’ plan “we will no longer have private insurance as we know it” – resulting in millions of Americans losing their private insurance.

Similar to previous debates, the discussion of immigration had Biden on the defensive over the 3 million undocumented immigrants that were deported under the Obama administration.

Former Housing and Urban Development Secretary Julian Castro, in particular, took aim at Biden, using the moment to attack Biden for “taking credit” for positive elements of the Obama legacy and distancing himself from criticism.

“He wants to take credit for Obama's work but not have to answer any questions,” Castro said of Biden.

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These attacks largely fell flat, as did Castro’s attempted jab at Biden’s age, and will surely not result in a post-debate polling spike for Castro that other candidates have experienced after attacking Biden during a debate.

“I stand with Barack Obama all eight years – good, bad, and indifferent,” Biden said in response to the immigration attacks, once again reverting to his campaign message of restoring, protecting and rebuilding the Obama-Biden record.

Aside from Castro’s attacks, throughout the entire night Sanders was the candidate who attacked Biden the most. He went after the former vice president not just on health care, but also on corporations, Biden’s vote in favor of the Iraq war as a senator, and trade.

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SURPRISE LOSER: BERNIE SANDERS

But while Sanders was one of the more vocal candidates, he did not deliver the performance he needed to in order to pull ahead of Biden or Warren in the polls. He was the night's other big loser.

Ultimately, Biden’s impressive – though not perfect – performance was a much-needed display of strength and preparedness and will likely solidify his frontrunner status.

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