Democratic frontrunner Joe Biden and close rivals Elizabeth Warren and Bernie Sanders have feuded over healthcare at the party's third debate.
The event in Houston, Texas, was the first time the three presidential hopefuls faced off in a debate.
Mr Biden attacked the feasibility of Mr Sanders' universal healthcare plan, Medicare for All, while Ms Warren and Mr Sanders defended the measure.
Only the 10 highest-polling Democrats in the field of 20 were on stage.
A former Vice-President, Mr Biden is leading current polls by a considerable margin, with Massachusetts Senator Ms Warren and Vermont Senator Mr Sanders in second and third. The rest of the field are polling in single figures.
A broad range of issues from climate change to gun control were debated, but it was healthcare which sparked the fieriest clashes.
Why is healthcare controversial?
The issue of how to reform the US healthcare system has become a point of disagreement between moderate and more progressive Democrats.
Mr Sanders and Ms Warren both back Medicare for All, which would expand an existing federally run programme for the elderly to cover all Americans in a single-payer insurance system.
Mr Biden criticised Mr Sanders' Medicare for All plan as being too expensive to work and said the country should focus on improving President Barack Obama's Affordable Care Act instead.
"I know the senator [Warren] says she's for Bernie. Well, I'm for Barack. I think Obamacare worked," Mr Biden said. "My plan costs a lot of money…but it doesn't cost $30tn (£24tn)."
Ms Warren defended the policy, saying families have to deal with exorbitant healthcare bills now, and only wealthier individuals and corporations would see increased costs from the plan.
Some of the lower polling candidates also attacked Mr Sanders and Ms Warren, with Minnesota Senator Amy Klobuchar saying that Medicare for All: "I don't think that's a bold idea. It's a bad idea."
How about gun control?
Former Texas congressman Beto O'Rourke, whose hometown El Paso was the site of a mass shooting that left 20 dead, was asked whether he supports confiscating assault-style rifles.
"Hell yes we're going to take your AR-15, your AK-47," Mr O'Rourke said to applause. "We're not going to allow it to be used against your fellow Americans anymore."
On gun control California Senator Kamala Harris drew President Trump into the debate, saying: "Obviously he didn't pull the trigger, but he's certainly been tweeting out the ammunition."
In their opening remarks most of the candidates attacked President Trump, blasting him for being a divisive leader and accusing him of racism.
What else happened?
Though some sparks flew there was also a lot of common ground between the candidates.
Here are some of the other memorable moments:
- Businessman Andrew Yang used his opening speech to announce he would be using donations to his campaign to start a "freedom dividend", giving $1,000 (£810) a month to 10 American families, prompting laughter from other candidates.
- New Jersey Senator Cory Booker, who is a vegan, was asked by a Spanish-speaking moderator whether he wanted Americans to stop eRead More – Source