In pictures: The Democratic debate in Ohio

Twelve presidential candidates take part in the Democratic debate in Westerville, Ohio, on Tuesday, October 15. The candidates, from left, are US Rep. Tulsi Gabbard; businessman Tom Steyer; US Sen. Cory Booker; US Sen. Kamala Harris; US Sen. Bernie Sanders; former Vice President Joe Biden; US Sen. Elizabeth Warren; South Bend, Indiana, Mayor Pete Buttigieg; businessman Andrew Yang; former US Rep. Beto O'Rourke; US Sen. Amy Klobuchar; and former Housing and Urban Development Secretary Julián Castro.

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Updated 11:59 AM EDT, Wed October 16, 2019

It was the most crowded debate stage in the history of US presidential primaries.

Twelve candidates shared the spotlight Tuesday at the Democratic debate in Westerville, Ohio, a suburb of Columbus. The event was hosted by CNN and The New York Times on the campus of Otterbein University.

This was the fourth Democratic debate of the campaign season, and it came three and a half months before the Iowa caucuses.

The first two debates had so many candidates that they had to be split up over two nights. But the Democratic National Committee raised the polling and fundraising thresholds that candidates need to qualify.

Those thresholds will be raised once again ahead of next month's debate in Georgia, so Tuesday might have been a make-or-break night for some of the lower-polling candidates.

Harris high-fives Sanders after <a href="https://www.cnn.com/politics/live-news/democratic-debate-october-2019/h_7a73060b9165d0ea7e2ce288b9767387" target="_blank">he said he's "healthy" and "feeling great"</a> following his heart attack on the campaign trail earlier this month. This was the first debate for Sanders since he had two stents inserted to clear a clogged artery.

Harris high-fives Sanders after he said he's "healthy" and "feeling great" following his heart attack on the campaign trail earlier this month. This was the first debate for Sanders since he had two stents inserted to clear a clogged artery.

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The candidates applaud Sanders as he talked about his health.

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Warren addresses Biden during the debate. She has been surging in the polls, challenging the front-runner status that Biden has held for months.

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Audience members watch the debate from the front row.

Gabriella Demczuk for CNN

<a href="https://www.cnn.com/2019/10/15/politics/joe-biden-hunter-ukraine-democratic-debate/index.html" target="_blank">Biden addressed allegations</a> against himself and his son, Hunter Biden, regarding Hunter's former seat on the board of a Ukrainian natural gas company. "My son did nothing wrong. I did nothing wrong," Biden said. President Donald Trump, his attorney Rudy Giuliani and his Republican allies have used Hunter Biden's foreign business ties to characterize the Bidens as corrupt. There is no evidence of wrongdoing by either Joe or Hunter Biden in Ukraine.

Biden addressed allegations against himself and his son, Hunter Biden, regarding Hunter's former seat on the board of a Ukrainian natural gas company. "My son did nothing wrong. I did nothing wrong," Biden said. President Donald Trump, his attorney Rudy Giuliani and his Republican allies have used Hunter Biden's foreign business ties to characterize the Bidens as corrupt. There is no evidence of wrongdoing by either Joe or Hunter Biden in Ukraine.

Maddie McGarvey for CNN

During the debate, Harris detailed how she, if elected president, <a href="https://www.cnn.com/politics/live-news/democratic-debate-october-2019/h_324661b2b061ab8a6515dadf96dc17cf" target="_blank">would handle state laws that violate Roe v. Wade.</a>"For any state that passes a law that violates the Constitution and in particular Roe v. Wade, our Department of Justice will review that law to determine if it is compliant with Roe v. Wade and the Constitution. And if it is not, that law will not go into effect," she said.

During the debate, Harris detailed how she, if elected president, would handle state laws that violate Roe v. Wade."For any state that passes a law that violates the Constitution and in particular Roe v. Wade, our Department of Justice will review that law to determine if it is compliant with Roe v. Wade and the Constitution. And if it is not, that law will not go into effect," she said.

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Yang looks to be called on during the debate. <a href="https://www.cnn.com/politics/live-news/democratic-debate-october-2019/h_b3f991ae16d87a40aa403db9b210b913" target="_blank">He's wearing a pin that says "MATH."</a> It's his campaign slogan: "Make America Think Harder." Yang, who has an economics degree from Brown University, has joked a lot about his love for math.

Yang looks to be called on during the debate. He's wearing a pin that says "MATH." It's his campaign slogan: "Make America Think Harder." Yang, who has an economics degree from Brown University, has joked a lot about his love for math.

Edward M. PioRoda/CNN

Westerville is the fourth debate stop of this campaign season. The first three were Miami, Detroit and Houston.

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Steyer, Booker and Harris take part in the debate. This was the first debate for Steyer, a billionaire hedge-fund founder who entered the race late.

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Sanders makes a point as Biden looks on.

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The debate's moderators during a commercial break. From left are CNN's Erin Burnett, CNN's Anderson Cooper and New York Times national editor Marc Lacey.

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Gabbard answers a question next to Steyer and Booker. Gabbard was absent from last month's debate because she didn't have the numbers to qualify.

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Biden and Booker talk during one of the breaks in the debate.

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Buttigieg <a href="https://www.cnn.com/politics/live-news/democratic-debate-october-2019/h_4f62b95fef11804bad3065983a55e426" target="_blank">argued for expanding the Affordable Care Act </a>rather than moving to Medicare for All, the government-backed health care program supported by Sens. Bernie Sanders and Elizabeth Warren.

Buttigieg argued for expanding the Affordable Care Act rather than moving to Medicare for All, the government-backed health care program supported by Sens. Bernie Sanders and Elizabeth Warren.

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Klobuchar looks to be called on during the debate.

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A view from the stage, looking out at the moderators and the audience.

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Castro, like many of his colleagues on stage, was critical of President Donald Trump's military withdrawal from Syria. "He has made a tremendous mistake, a total disaster in Syria," Castro said.

Gabriella Demczuk for CNN

<a href="https://www.cnn.com/politics/live-news/democratic-debate-october-2019/h_35dd40d2601f6eca9a10740018148cc4" target="_blank">Booker warned Democrats</a> against "tearing each other down" over their different plans. "I have seen this script before. It didn't work in 2016 and it will be a disaster for us in 2020," he said.

Booker warned Democrats against "tearing each other down" over their different plans. "I have seen this script before. It didn't work in 2016 and it will be a disaster for us in 2020," he said.

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Warren playfully puts her dukes up during a break in the debate.

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The debate took place at Otterbein University. Trump carried Ohio by 8 percentage points in 2016.

Edward M. PioRoda/CNN

O'Rourke is seen on a television monitor backstage.

Gabriella Demczuk for CNN

Biden <a href="https://www.cnn.com/politics/live-news/democratic-debate-october-2019/h_a5d8d459d4e71bded4a73b38d7592678" target="_blank">defended his age</a> during the debate: "Look, one of the reasons I'm running is because of my age and my experience, with it comes wisdom. We need someone to take office this time around who on day one can stand on the world stage, command the respect of world leaders from (Russian President Vladimir) Putin to our allies, and know exactly what has to be done to get this country back on track."

Biden defended his age during the debate: "Look, one of the reasons I'm running is because of my age and my experience, with it comes wisdom. We need someone to take office this time around who on day one can stand on the world stage, command the respect of world leaders from (Russian President Vladimir) Putin to our allies, and know exactly what has to be done to get this country back on track."

John Nowak/CNN