Twelve presidential candidates gathered all on one stage in Westerville, Ohio for the fourth DNC primary debate on Tuesday, October 15.

Issues including healthcare, automation, and trade — all of which have impacted jobs in Ohio — took center stage, with all the candidates promising to strengthen unions and push for fairer trade deals.

Sen. Elizabeth Warren has been surging both in Democratic primary polls and in fundraising and was attacked like a frontrunner in the debate over her stances on every issue from healthcare to the wealth tax.

Mayor Pete Buttigieg, in particular, went on the attack and was far more assertive than in previous debates, successfully landing punches on multiple candidates.

Here are the top breakout moments from Tuesday night's debate.

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Twelve presidential candidates gathered all on one stage in Westerville, Ohio for the fourth DNC primary debate hosted by CNN and The New York Times on Tuesday, October 15.

The debate marked billionaire financier Tom Steyer's debut on the national stage, and possibly the last hurrah for candidates like Julian Castro, Rep. Tulsi Gabbard, former Rep. Beto O'Rourke, and Sen. Amy Klobuchar, who are at risk of not qualifying for the next debate in November.

Issues including healthcare, automation, and trade — all of which have impacted jobs in Ohio — took center stage, with all the candidates promising to strengthen unions and push for fairer trade deals.

The candidates also extensively discussed foreign policy and US involvement abroad amid the US' dramatic withdrawal from Syria, abandoning the Kurdish people — who have been crucial partners in the fight against ISIS — and giving the terror group an opening to make a resurgence.

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Sen. Elizabeth Warren has been surging both in Democratic primary polls and in fundraising and was attacked like a frontrunner in the debate over her stances on every issue from healthcare to the wealth tax.

An NBC News analysis found that former Vice President Joe Biden — who previously owned the mantle of the frontrunner — was attacked just twice in the debate, while Warren was attacked 16 separate times, the most of any candidate.

Mayor Pete Buttigieg, in particular, went on the attack and was far more assertive than in previous debates, successfully landing punches on Warren over healthcare, on Gabbard over foreign policy, and on O'Rourke over gun control policy.

Here's a rundown of the seven biggest moments of the debate: