Open this photo in gallery Former U.S. vice president Joe Biden, left, looks down and grips his lectern as Sen. Kamala Harris speaks about her personal experience and his opposition to school busing in the 1970s during the Democratic presidential debate, in Miami, on June 27, 2019. DOUG MILLS/The New York Times News Service

Kamala Harris has drawn the first blood of the battle for the Democratic presidential nomination, forcing front-runner Joe Biden on the defensive over his record on racial segregation.

In the most bruising exchange of Thursday night’s debate, the California Senator took aim at the former vice-president for holding up his ability to work with segregationist senators in the 1970s as a model of “civility” in politics.

Then, she hammered him for not supporting “desegregation busing,” a method used to ensure more equal numbers of white and black students attended the same schools.

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“It was actually very hurtful to hear you talk about the reputations of two United States senators who built their reputation and career on the segregation of race in this country. And it was not only that, but you also worked with them to oppose busing,” she said.

In first 2020 debate, Democrats spar over health care and immigration

“There was a little girl in California who was a part of the second class to integrate her public schools, and she was bused to school every day. And that little girl was me."

The showdown in Miami was the first opportunity for several of the race’s top candidates to go head-to-head, with Vermont Senator Bernie Sanders and South Bend, Ind., Mayor Pete Buttigieg among the other leading contenders on stage. The Democratic field is so large that the party split the candidates into two groups of 10; Senators Elizabeth Warren and Cory Booker were among those who debated the previous night.

Mr. Biden, who has comfortably led in the polls since announcing his candidacy two months ago, appeared to struggle to formulate a response to Ms. Harris. He said her attack was “a mischaracterization of my position across the board,” took a dig at her career as a district attorney and meandered when he tried to explain his position on busing.

“I did not praise racists, that is not true,” Mr. Biden said. “If we want to have this campaign litigated on who supports civil rights and whether I did or not, I’m happy to do that. I was a public defender. I didn’t become a prosecutor … in terms of busing, the busing, I never – you would have been able to go to school the same exact way because it was a local decision made by your city council.”

Mr. Biden earlier this month cited his relationships with former senators James Eastland and Herman Talmadge, both segregationist Democrats, as a good example of how to work with people with whom he disagreed.

“There was some civility,” he told the audience at a fundraiser. “We got things done.”

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In the 1970s, Mr. Biden also supported legislation to curtail federal power to order schools to use busing as an integration method.

Ms. Harris, who needed to fire up her campaign after consistently underperforming expectations, would not let up the pressure.

“Do you agree today that you were wrong to oppose busing in America then?” she said.

“I did not oppose busing in America. What I opposed is busing ordered by the Department of Education,” Mr. Biden replied, saying that busing was “a local decision.”

“That’s where the federal government must step in,” Ms. Harris said. “There are moments in history where states fail to preserve the civil rights of all people."

Mr. Biden cited the debate clock to end the exchange. “My time is up, I’m sorry,” he said.

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The moment is certain to spotlight criticisms that the 76-year-old former vice-president is out of touch with a party increasingly concerned by issues of social justice, and off his game politically. Most of his answers Thursday were restrained, and he occasionally rambled.

Mr. Biden faced another difficult moment when asked about his support for the 2003 invasion of Iraq. He did not answer the question directly, but instead cited his later work with former president Barack Obama withdrawing troops from the country. He also said he hoped to end the war in Afghanistan, which the Obama administration had continued.

“I was responsible for getting 150,000 combat troops out of Iraq, and my son was one of them. I also think we should not have combat troops in Afghanistan. It’s long overdue,” Mr. Biden said.

In a contrast with Mr. Biden’s defence of his record on race, Mr. Buttigieg expressed contrition for failing to build a more diverse police force in South Bend, where the fatal shooting of Eric Logan, a black man, by a white officer has reignited anger at police brutality towards people of colour.

“I couldn’t get it done. My community is in anguish right now,” Mr. Buttigieg said when asked why such a small proportion of police in his city are black. “There’s a wall of mistrust built up one racist act at a time."

Mr. Sanders, for his part, relied on a string of spicy sound bites to buttress his position as the candidate of the left.

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He branded President Donald Trump “a pathological liar and a racist.” And he argued that only major changes, from putting every American on a government-funded health care plan to offering free university tuition, can close America’s widening wealth gap.

“Nothing will change unless we have the guts to take on Wall Street, the insurance industry, the pharmaceutical industry, the military-industrial complex and the fossil-fuel industry,” Mr. Sanders said.

At one point, he found himself gently rebuked by Ms. Harris when he, New York Senator Kirsten Gillibrand and California Congressman Eric Swalwell all tried to talk over each other.

“Hey guys, you know what? America does not want to witness a food fight. They want to know how we’re going to put food on their table,” she said.

Mr. Swalwell tried to break through for his long-shot campaign by playing attack dog. He demanded Mr. Biden “pass the torch” to a new generation of political leaders. He needled Mr. Sanders into promising to spend government funds to buy back assault rifles from gun owners. And he excoriated Mr. Buttigieg for not cleaning house in his police force. “You should fire the chief,” he said.

Other low-polling candidates on the stage – former Colorado governor John Hickenlooper, former senator Michael Bennet and entrepreneur Andrew Yang – had difficulty making an impression as the front-runners battled it out.

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Self-help author Marianne Williamson took an unusual tack to cut through the noise, arguing that Democrats should stop putting forward detailed policy proposals and instead “harness love for political purposes” to win the election.

“It’s really nice that we’ve got all these plans,” she said. “But if you think we’re going to beat Donald Trump just by having all these plans, you got another thing coming.”

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