Twelve of the 2020 Democratic presidential candidates took the stage in Westerville, Ohio, on Tuesday night for the fourth round of presidential debates.

South Bend Mayor Pete Buttigieg was the clear winner of Tuesday's debate. He was far more aggressive than usual and it paid off.

Former Vice President Joe Biden and former Rep. Beto O'Rourke of Texas were the clear losers of the debate. They lacked energy and struggled to clearly articulate their stances.

Sen. Elizabeth Warren wasn't necessarily a winner or a loser, but the candidates really piled on her for the first time there were pros and cons to this.

Sens. Bernie Sanders and Amy Klobuchar, as well as tech entrepreneur Andrew Yang, all had good nights and stood out in different ways.

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The 2020 Democratic presidential candidates took the stage in Westerville, Ohio, on Tuesday night for the fourth round of presidential debates.

With 12 candidates on the stage, the debate was the most crowded in the history of US presidential primaries.

This was the first debate to occur since the launch of an impeachment inquiry into President Donald Trump in the House, and it was a huge topic from the start.

While the candidates were unified in their opposition to Trump, they differed strongly on key issues like health care.

After several hours of heated exchanges, there were a number of clear winners and losers from Tuesday night's debate.

The winners

South Bend Mayor Pete Buttigieg listens during the fourth U.S. Democratic presidential candidates 2020 election debate at Otterbein University in Westerville, Ohio, on October 15, 2019. Shannon Stapleton/Reuters

South Bend Mayor Pete Buttigieg had the strongest performance of the night. He was aggressive and had the second most attacks on other candidates of all of those on the stage, according to an analysis from NBC News. This can be a risky strategy, but it paid off for Buttigieg on issues like foreign policy.

Buttigieg, a veteran of the war in Afghanistan, had a heated exchange with Rep. Tulsi Gabbard, a veteran of the Iraq War, on Trump's recent decision to abandon US-allied Kurdish forces in Syria.

Gabbard contended the US never should've been involved in Syria in the first place, making nebulous references to a "regime change war."

Buttigieg told her she was "dead wrong," offering an impassioned rebuke of Trump's "betrayal" of Kurdish forces who bore the brunt of the US-led campaign against ISIS. The South Bend, Indiana, mayor warned that Trump's decision could to massive damage to US credibility and send a dangerous message to the wider world.

At 37, Buttigieg is the youngest candidate running for the 2020 Democratic presidential nomination, but he came off as a seasoned, intrepid politician on Tuesday night.

Read more: Pete Buttigieg and Tulsi Gabbard, the only military vets on the Democratic debate stage, duke it out over US action in Syria

Sen. Bernie Sanders also had a strong performance on Tuesday after recently being hospitalized due to a heart attack. Sanders was energetic, focused, and jovial during the debate, which is precisely the boost his campaign needed amid concerns over his health. The Vermont senator's points on health care, wealth inequality drew strong applause from the audience, while a joke he made about not being on marijuana prompted uproarious laughter.

And though it wasn't a direct aspect of the debate, Sanders managed to dominant the conversation online toward the end of it after the news broke Democratic Rep. Alexandria Ocasio-Cortez is poised to endorse his campaign.

Read more: Alexandria Ocasio-Cortez endorses Bernie Sanders for president

Meanwhile, Sen. Amy Klobuchar and tech entrepreneur Andrew Yang both get honorable mention for their performances on Tuesday.

Klobuchar arguably had her best debate yet, with a number of sharp one-liners and coming in third in terms of speaking time out of all of those on the stage, according to an analysis from The New York Times.

Yang was closer to the bottom of the pack in terms of speaking time but still had a strong presence in the debate given the heavy focus on universal basic income, the policy at the center of his platform.

The losers

Democratic presidential candidate and former Rep. Beto O'Rourke listens during the fourth U.S. Democratic presidential candidates 2020 election debate in Westerville, Ohio, on October 15, 2019. REUTERS/Shannon Stapleton

Former Vice President Joe Biden and former Texas Rep. Beto O'Rourke were the biggest losers of the night.

Biden stumbled through many of his responses, and offered a lukewarm defense of criticism over his son's work for a Ukrainian natural gas company while he was vice president. Trump has alleged that Biden inappropropriately urged Ukraine to fire a prosecutor who at one point investigated the company, but there's no evidence of this or any wrongdoing on the part of the former vice president or his son.

This is all tied to the impeachment inquiry into Trump, which is linked to a July 25 phone call in which Trump urged Ukraine's president to investigate the Bidens. As the inquiry and related Ukraine scandal escalate, Trump's baseless accusations against the Bidens have gained steam on conservative media outlets and among Republicans.

Biden has struggled to fend off these attacks, and that trend continued on the debate stage on Tuesday.

O'Rourke, whose campaign has been dwindling in recent months, barely had a presence during the debate. He offered a tepid defense of his proposal to ban AR-15s, and that was perhaps the only moment he stood apart from the rest of the candidates.

Gabbard, who had threatened to boycott the debate, was also a loser. She echoed talking points of the Syrian and Russian governments with the false assertion the US has been engaged in "regime change war" in Syria, when its primary purpose there has been to combat ISIS. Gabbard's performance further fueled the perception she's an apologist for Syrian President Bashar al-Assad.

Meanwhile, it was easy to forget that former HUD Secretary Julián Castro and billionaire Tom Steyer were on the stage.

Warren wasn't a winner or a loser, but had a big night in multiple ways

Democratic presidential candidate Senator Elizabeth Warren speaks during the fourth U.S. Democratic presidential candidates 2020 election debate at Otterbein University in Westerville, Ohio U.S. Reuters

After several weeks of climbing to the top of both state and national polls, Sen. Elizabeth Warren was treated as the frontrunner during the debate. She had the most speaking time by far (nearly 23 minutes) and was attacked far more than any other candidate on the stage (16 times).

The amount of attention Warren received feeds into the growing perception she's supplanting Biden as the top contender for the 2020 Democratic nomination.

The Massachusetts senator seems to still be adjusting to this, however, as she struggled to fend off some of the attacks aimed at her by other candidates — particularly regarding her health care plan and whether it means raising taxes for the middle class.

Regardless, Warren came out of the debate looking like one of the most important candidates in the field, if not the most important, and that's always beneficial to a campaign. Warren was neither a winner nor a loser on Tuesday.

Sens. Cory Booker and Kamala Harris had decent nights, but struggled to break through the large crowd on the stage. Both ended up in the middle of the pack in terms of speaking time, and neither had many standout moments. Like Warren, they were neither winners nor losers. But unlike Warren, they were not key figures in the night's proceedings.