Here are five memorable moments from the event:
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1. Gabbard and Harris clash over Democratic Party criticism.
While answering a question about her past criticism of 2016 Democratic presidential nominee Hillary Clinton, Gabbard elaborated on what she has previously described as "the rot that has sickened the Democratic Party."
"Our Democratic Party, unfortunately, is not the party that is of, by and for the people," she said. "It is a party that has been and continues to be influenced by the foreign policy establishment in Washington, represented by Hillary Clinton and others' foreign policy, by the military industrial complex and other greedy corporate interests."
Gabbard added that she wants "to be the Democratic nominee that rebuilds our Democratic Party, takes it out of their hands, and truly puts it in the hands of the people of this country."
When asked to respond, Harris didn't hold back.
"I think that it's unfortunate that we have someone on this stage who is attempting to be the Democratic nominee for president of the United States, who, during the Obama administration, spent four years full time on Fox News criticizing President Obama," Harris began.
"That's ridiculous, Sen. Harris," Gabbard interjected. "That's ridiculous."
Harris continued: "... who has spent full time criticizing people on this stage as affiliated with the Democratic Party, when Donald Trump was elected – not even sworn in – buddied up to Steve Bannon to get a meeting with Donald Trump in the Trump Tower, fails to call a war criminal by what he is as a war criminal, and then spends full time during the course of this campaign, again, criticizing the Democratic Party."
Gabbard fired back, claiming Harris was "continuing to traffic in lies and smears in innuendos" and would likely "continue the Bush-Clinton-Trump foreign policy of regime change wars."
>> Watch the exchange here
2. Gabbard and Buttigieg spar over foreign policy.
Gabbard also criticized Buttigieg during Wednesday's debate, arguing that the mayor from Indiana lacked foreign policy experience.
"I think the most recent example of your inexperience in national security and foreign policy came from your recent careless statement about how you as president would be willing to send our troops to Mexico to fight the cartels," Gabbard said.
Buttigieg shot back, saying Gabbard had taken his comments "out of context."
"I was talking about U.S.-Mexico cooperation," he said. "We've been doing security cooperation with Mexico for years, with law enforcement cooperation and a military relationship that could continue to be developed with training relationships, for example. Do you seriously think anybody on this stage is proposing invading Mexico?"
"That's not what I said," Gabbard interjected.
Buttigieg then questioned Gabbard's judgment, particularly over her meeting with Syrian President Bashar Assad.
"I have, in my experience – such as it is, whether you think it counts or not since it wasn't accumulated in Washington – enough judgment that I would not have sat down with a murderous dictator like that," he said.
>> See the moment here
3. Booker blasts Biden's position on marijuana laws.
While discussing the issues that impact black voters, Booker took aim at Biden, who, according to CNN, said last weekend that he wouldn't back legalizing marijuana nationwide until he sees more evidence that pot isn't a "gateway drug."
"I have a lot of respect for the vice president. He has sworn me into my office as a hero," Booker said. "This week, I hear him literally say that I don't think we should legalize marijuana. I thought you might have been high when you said it."
Following the remark, which drew laughs from audience members, Booker continued on a more serious note.
"Marijuana in our country is already legal for privileged people," he said. "The war on drugs has been a war on black and brown people."
Biden later clarified that although he still has questions about legalizing marijuana, he does support decriminalizing the drug and expunging offenders' records.
>> Watch the clip here
4. Biden's comment about African American support sparks confusion.
As Biden and Booker continued to discuss race, one remark from the former vice president left some fellow candidates and viewers scratching their heads.
"I'm part of that Obama coalition," Biden began. "I come out of a black community, in terms of my support. If you notice, I have more people supporting me in the black community that have announced for me because they know me; they know who I am."
Some of those supporters, he said, include "three former chairs of the black caucus" and "the only African American woman that'd ever been elected to the United States Senate," former Sen. Carol Moseley Braun of Illinois.
Booker and Harris, a black, female senator, immediately took issue with Biden's comments, interjecting, "That's not true."
"The other one is here," Harris pointed out, laughing and shrugging.
Biden continued: "No, I said the first. I said the first African American woman."
>> Watch the moment here
5. Klobuchar says women are held to a "higher standard."
When asked to clarify a previous comment about whether a woman with Buttigieg's experience would be on the debate stage, Klobuchar elaborated on the challenges facing women in politics.
"I've made very clear I think that Pete is qualified to be up on this stage, and I am honored to be standing next to him, but what I said was true," she began. "Women are held to a higher standard. Otherwise, we could play a game called 'Name Your Favorite Woman President,' which we can't do, because it has all been men."
She added: "We have to work harder, and that's a fact."
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