(Bloomberg) -- California Senator Kamala Harris took control of an animated Democratic debate, directly confronting front-runner Joe Biden and accusing him of being insensitive to the plight of African-Americans, a key constituency in the party’s nomination contest.The former vice president was put on the defense several times by the other candidates during the two-hour forum Thursday in Miami over his past stances and current positions on issues such as health care and immigration. But it was Harris who landed perhaps the toughest blows as she interjected during a discussion about race.As the only candidate of African-American heritage on the stage, Harris told Biden that she doesn’t believe he is a racist, but it was “hurtful” to hear him speak recently about working with two pro-segregation senators four decades ago to oppose federal guidelines on busing to integrate public schools. Harris recalled that at the time she was a “little girl” in California who was in just the second class to integrate schools in Berkeley.“On this subject, it cannot be an intellectual debate among Democrats. We have to take it seriously. We have to act swiftly,” she said. “There are moments in history where states fail to preserve the civil rights of all people.”Biden responded that he didn’t praise racists and accused Harris of mischaracterizing his positions. He defended his record on civil rights starting as a public defender and not, like Harris, choosing to work on the other side as a prosecutor.Biden’s Defense“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,” Biden said. “The bottom line here is, look, everything I have done in my career, I ran because of civil rights, I continue to think we have to make fundamental changes in civil rights.”It was the sharpest exchange in two nights of Democratic debates, which overall was more combative than the event the night before. It was one of several episodes in a strong performance by Harris as she aims to gain ground on Biden, Bernie Sanders and Elizabeth Warren, who are ahead of her in polls.The main target of attack for all the candidates was President Donald Trump, as Biden and nine other hopefuls sought to demonstrate for voters the stark choice they will have in the 2020 election.Targeting Trump“Donald Trump thinks Wall Street built America. Ordinary middle-class Americans built America,” Biden said. “Donald Trump has put us in a horrible situation.”Sanders said “the American people understand that Trump is a phony, that Trump is a pathological liar and a racist, and that he lied to the American people during his campaign.”Early on, several of the candidates turned away from Trump and focused on each other in a series of testy exchanges, talking over and at each other, until Harris stepped in.“America does not want to witness a food fight, they want to know how we are going to put food on their table,” Harris said, putting an end to the squabble. It had begun with a generational brawl, as California Representative Eric Swalwell, 38, argued for generational change atop the Democratic Party, a jab at Biden, 76.Generational ChangeIt is time to “pass the torch,” Swalwell said, recalling seeing Biden speak when he was just a child. Given a chance to respond to an attack, Biden said he wasn’t giving up. “I’m still holding onto that torch,” he said, before launching into a discussion of his education plans. Sanders also tried to interject, telling the moderators: “I’m part of Joe’s generation, let me respond.”Pete Buttigieg, the mayor of South Bend, Indiana, questioned Sanders’s proposal for free college education by saying only low-and middle-income students should be helped because “I just don’t believe it makes sense to ask working-class families to subsidize even the children of billionaires.” He also was asked to defend his handling of shooting of a black man by a white South Bend police officer and said systemic racism “threatens the well-being of every community.”Thursday night’s debate in Miami was the first side-by-side appearance of the campaign for Biden and Sanders, who are leading in most polls, and the contrasts between the two were being carefully watched as they charted starkly different paths to the party’s nomination and beyond that, the 2020 general election.Contrasting PositionsSanders, an independent senator from Vermont, had already begun highlighting where he diverges with Biden, aiming to expose the former vice president’s weaknesses with left-leaning voters on issues such as Medicare for All and the Green New Deal.Biden, 76, represents the Democrats’ centrist wing, while Sanders, 77, is running on a platform he describes as democratic socialism. But the two men largely ignored each other on the debate stage.But Harris, 54, a former California attorney general and San Francisco district attorney, who was the most assertive candidate on either debate stage this week and expressed her policy positions with personal stories.“We have to think about how this affects real people,” Harris said during a discussion about health care, describing a parent taking a sick child to the emergency room knowing there will be a $5,000 insurance deductible.“That’s what insurance companies are doing in America today,” Harris said.The debate gave voters a chance to see four of the five top-polling candidates for the Democratic nomination interacting with one another, plus half a dozen candidates who’ve averaged 1% or less in key state and national polling.Biden and Sanders, two white male septuagenarians, were positioned at podiums in the middle of the stage, flanked by younger, more diverse opponents. On one side was the 37-year-old openly gay Buttigieg, and on the other Harris.Warren, a Massachusetts senator who’s edging out Sanders for second in a growing number of polls, was the only candidate among the leading contenders who ended up on Wednesday’s debate stage.There was little discussion of Trump during Wednesday’s debate, but with Biden and Sanders more explicitly building their campaigns around their arguments of electability the president was a more central foil on Thursday. Although Trump was at an international summit in Osaka, Japan, it was clear he -- or his staff -- was tuned in.During a discussion about health care, the candidates were asked whether their plans would provide coverage to undocumented immigrants. All raised their hands. Biden said the U.S. can’t let people who are sick go uncovered.Trump then tweeted: “All Democrats just raised their hands for giving millions of illegal aliens unlimited healthcare. How about taking care of American Citizens first!? That’s the end of that race!’’While the first round of debating isn’t likely to shake up the race, a handful of middle-tier candidates including New Jersey Senator Cory Booker and former Housing and Urban Development Secretary Julian Castro were able to breathe new oxygen into their bids with strong performances on Wednesday night.Senators Kirsten Gillibrand of New York and Michael Bennet, of Colorado, as well as former Colorado Governor John Hickenlooper, all of whom rarely crack 1% in polls, were hoping to do the same in Thursday’s debate.The stage also featured two candidates who have never held elected office: former tech entrepreneur Andrew Yang, whose core promise is to establish a universal basic income of $12,000 for every American adult, and spirituality author Marianne Williamson.\--With assistance from Tyler Pager and Sahil Kapur.To contact the reporters on this story: Jennifer Epstein in Miami at jepstein32@bloomberg.net;Mark Niquette in Miami at mniquette@bloomberg.netTo contact the editors responsible for this story: Joe Sobczyk at jsobczyk@bloomberg.net, Ros KrasnyFor more articles like this, please visit us at bloomberg.com©2019 Bloomberg L.P.