Democratic frontrunner Joe Biden and close rivals Elizabeth Warren and Bernie Sanders have feuded over healthcare at the party’s third debate.
The debate in Houston, Texas, is the first time the three presidential hopefuls have been on stage together.
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 are on stage.
The eventual Democratic White House nominee will be announced at the party convention next July, before the presidential election in November.
Gun control, immigration, climate change and tariffs were also debated – but healthcare saw the fieriest clashes.
What is the healthcare debate?
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 Senator Amy Klobuchar saying of Medicare for All: “I don’t think that’s a bold idea. It’s a bad idea.”
How about gun control?
Former 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 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 the opening remarks most of the candidates attacked President Trump, blasting him for being a divisive leader and accusing him of racism.
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.
Who’s on stage?
This is the full line-up for the debate, which, unlike the two prior events will take place over one night as only 10 candidates fulfilled the stricter polling and donor requirements.
- Minnesota Senator Amy Klobuchar
- New Jersey Senator Cory Booker
- South Bend, Indiana, Mayor Pete Buttigieg
- Vermont Senator Bernie Sanders
- Former Vice-President Joe Biden
- Massachusetts Senator Elizabeth Warren
- California Senator Kamala Harris
- Entrepreneur Andrew Yang
- Former Texas Congressman Beto O’Rourke
- Former Obama housing secretary Julian Castro
There are 10 others left in the race, and four have dropped out.