Healthcare opened up clear differences between frontrunners but Donald Trump was the key target amid a more conciliatory tone

Confrontation erupted on the debate stage as energized frontrunner Joe Biden verbally sparred with progressives Elizabeth Warren and Bernie Sanders, revealing deep divisions over healthcare, immigration, foreign policy and how far left the party should move.

But the debate also took a more conciliatory tone than previous ones as rival candidates praised each other and concentrated much of their fire in the direction of Donald Trump.

Round three of the presidential debates, held on Thursday at Texas Southern University, a historically black college in Houston, featured all of the top contenders for the party’s nomination on a single stage for the first time. The sprawling metropolis, one of the most diverse cities in America, reflected the diversity of the Democratic field, which featured women, people of color and a gay man.

Over the course of three hours, Democrats debated a central question animating the primary contest: do they want to return to an era of politics that existed before the Trump presidency or do they favor policies that go far beyond the last administration?

“I stand with Barack Obama, all eight years, the good, bad and indifferent,” Biden said, defending himself against an attack on his record.

﻿The ABC News debate opened with a clash over healthcare, one of the sharpest differences among the candidates and a top priority for Democratic voters.

Wrapping himself in Obama’s legacy, the former vice-president confronted his progressive challengers over the cost of Medicare for All, which would cover every American under a government health plan and essentially eliminate private insurance, accusing Warren of not being forthcoming about whether the plan would raise taxes on the middle class.

“I know the senator says she’s for Bernie,” he said of Warren’s support for Sanders’ Medicare for All healthcare plan. “Well, I’m for Barack. I think the Obamacare worked.”

Facebook Twitter Pinterest Kamala Harris makes a point flanked by Elizabeth Warren and Andrew Yang. Photograph: Heidi Gutman/ABC via Getty Images

Biden, sandwiched between Sanders and Warren on stage, suggested that Warren’s plan to raise taxes on the wealthiest Americans by 2% falls short of the estimated $30tn it would cost to implement a Medicare for All system. Warren shot back: “I’ve never actually met anybody who likes their health insurance company.”

The former vice-president also challenged Sanders’ proposal to force employers to effectively pay out union members for any savings from a shift to a single-payer health system. “For a socialist, you’ve got a lot more confidence in corporate America than I do,” he said.

A highly anticipated showdown between Biden and Warren, who is steadily gaining on him in the polls, never fully materialized into open warfare. By contrast, Sanders came prepared to draw sharp contrasts with Biden on trade and foreign policy. The Vermont Senator condemned Biden for his vote in favor of the Iraq war. “The truth is, the big mistake, the huge mistake, and one of the big differences between you and me, I never believed what Cheney and Bush said about Iraq,” said Sanders, who opposed it.

But the conversation broadened from the dynamic of the top three, leading to one of the sharpest skirmishes of the evening between Biden and former housing and urban development secretary Julián Castro.

In a testy back-and-forth, Castro, 44, alluded to voter concerns about Biden’s age when he continued to press the former vice-president about whether he had forgotten a piece of his healthcare plan. If elected, Biden would be the oldest first-term president at 78.

Play Video 0:36 Castro questions Biden's memory during third Democrat debate – video

“Are you forgetting what you said two minutes ago?” Castro asked, eliciting gasps from the audience. Castro, who also served the Obama administration, boasted: “I’m fulfilling the legacy of Barack Obama and you’re not.”

As they sparred, Pete Buttigieg, the 37-year-old mayor of South Bend, Indiana, appealed for unity.

“This is why the presidential debates are becoming unwatchable,” he said. “This reminds everybody of what they cannot stand about Washington.”

“That’s called an election,” Castro snapped back. “This is what we’re here for.”

Questions about gun violence, immigration and trade with China also revealed a difference of opinion and a hefty dose of criticism of Trump. The California senator Kamala Harris accused the president of using “hate, intimidation, fear”, to divide the country. The New Jersey senator Cory Booker called Trump “racist”.

Former Texas representative Beto O’Rourke and Castro, the two Texans in the race, spoke emotionally about the mass shootings that rocked the state last month. In El Paso, 22 people, many of them Latino, were killed at a Walmart by a gunman who invoked Trump’s language in describing the motivation for his attack. Weeks later, a gunman killed seven people during a shooting spree between the Texas cities of Odessa and Midland.

“A few weeks ago, a shooter drove 10 hours, inspired by this president, to kill people who look like me,” Castro said. He called white supremacy a “growing threat to this country”.

Play Video 1:42 Beto O'Rourke on gun control: 'Hell yes, we’re going to take your AR-15' – video

O’Rourke did not shy away from saying he would require citizens to turn in their military-style weapons, despite Republicans’ frequent accusations that Democrats are coming to take Americans’ guns.

“Hell yes, we’re going to take your AK-47,” O’Rourke said in one of the biggest lines of the night. O’Rourke was also the recipient of praise from other candidates on the stage – including Biden and Castro – for his actions in dealing with the tragedy in his native El Paso.

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Both Warren and Biden are leading contenders for the Democratic nomination, but they represent dueling visions for the party. Biden is a relative moderate with plans that would build on the work of the Obama administration and Warren is a progressive who has called for “big, structural change” through an expanding portfolio of detailed policy plans.

There were also moments of levity in Houston. Harris erupted in laughter after drawing a comparison between Trump and the “really small dude” behind the curtain in the Wizard of Oz.

Facebook Twitter Pinterest Elizabeth Warren has called for ‘big, structural change’. Photograph: Josh Edelson/AFP/Getty Images

Entrepreneur Andrew Yang, the only non-politician on stage, surprised his rivals – and viewers – when he announced a plan to give away $1,000 a month to 10 families over the next year, a gambit aimed at promoting his universal basic income signature campaign proposal.

“That was original,” Buttigieg said. “I’ll give you that.”

Later in the evening, in a moment that would have been unlikely even just a decade ago, Buttigieg spoke movingly about his decision to come out publicly as gay in 2015.

“I came back from the deployment and realized that you only get to live one life and I was not interested in not knowing what it was like to be in love any longer. So I just came out,” he said.

“What happened was that when I trusted voters to judge me based on the job that I did for them, they decided to trust me and they re-elected me with 80% of the vote.”