It was one of several moments that left the 76-year-old Biden, who entered the night as his party’s fragile front-runner, on the defensive as he worked to convince voters across America that he’s still in touch with the Democratic Party of 2020 and best-positioned to deny President Donald Trump a second term.

“I do not believe you are a racist,” Harris said to Biden, though she described his record of working with Democratic segregationist senators on non-race issues as “hurtful.”

Biden called Harris’ criticism “a complete mischaracterization of my record.” He declared, “I ran because of civil rights” and later accused the Trump administration of embracing racism.

The debate marked an abrupt turning point in a Democratic primary in which candidates have largely tiptoed around each other, focusing instead on their shared desire to beat Trump. But the debate revealed just how deep the fissures are within the Democratic Party eight months before primary voting begins.

Thursday’s debate, like the one a night earlier, gave millions of Americans their first peek inside the Democrats’ unruly 2020 season.

The showdown featured four of the five strongest candidates   according to early polls, at least. Those are Biden, Sanders, Pete Buttigieg of Indiana and Harris. Massachusetts Sen. Elizabeth Warren, who debated Wednesday night, is the fifth.

There are so many candidates lining up to take on Trump that they do not all fit on one debate stage   or even two. Twenty Democrats debated on national television this week in two waves of 10, while a handful more were left out altogether.

The level of diversity on display was unprecedented for a major political party in the United States. The field features six women, two African Americans, one Asian American and two men under 40, one of them openly gay.

Yet in the early days of the campaign, two white septuagenarians are leading the polls: Biden and Vermont Sen. Sanders.

Thursday’s slate of candidates   and the debate itself   highlighted the unprecedented diversity of the Democratic Party’s 2020 class.

South Bend, Indiana Mayor Pete Buttigieg, a 37-year-old gay former military officer, is four decades younger than Sanders, and has been framing his candidacy as a call for generational change in his party. Harris is the only African American woman to qualify for the presidential debate stage. Any of the three women featured Thursday night would be the first ever elected president.

Buttigieg faced tough questions about a racially charged recent police shooting in his city in which a white officer shot and killed a black man, Eric Logan.

Buttigieg said an investigation was underway, and he acknowledged the underlying racial tensions in his city and others. “It’s a mess,” he said plainly. “And we’re hurting.”

One of the lesser-known candidates on stage, California Rep Eric Swalwell, called on Buttigieg to fire his police chief, even though the investigation was only beginning.

Swalwell also took a swipe at Biden’s advanced age. Either Biden or Sanders would be the oldest president ever elected.

“Joe Biden was right when he said it was time to pass the torch to a new generation of Americans 32 years ago,” Swalwell jabbed.

Biden responded: “I’m still holding on to that torch.”

The party’s broader fight over ideology played a back seat at times to the racial and generational divisions. But calls to embrace dramatic change on immigration, health care and the environment were not forgotten.

Sanders slapped at his party’s centrist candidates, vowing to fight for “real change.”

Biden downplayed his establishment leanings. For example, the former vice president, along with the other candidates on stage, raised his hand to say his health care plan would provide coverage for immigrants in the country illegally.

Former Colorado Gov. John Hickenlooper predicted that an aggressive lurch to the left on key policies would ultimately hurt Democrats’ quest to defeat Trump.

“If we don’t clearly define we are not socialists, the Republicans are going to come at us every way they can and call us socialists,” he warned.

Others on the stage Thursday night included Sens. Kirsten Gillibrand of New York and Michael Bennet of Colorado, New York businessman Andrew Yang and author and social activist Marianne Williamson.

The showdown played out in Florida, a general election battleground that could well determine whether Trump wins a second term next year.

Biden sought to sidestep the intraparty divisions altogether, training his venom on Trump.

“Donald Trump thinks Wall Street built America. Ordinary middle-class Americans built America,” said the former vice president. He added: “Donald Trump has put us in a horrible situation. We do have enormous income inequality.”

Biden’s strategy is designed to highlight his status as the front-runner, and as such, the Democrat best positioned to take down the president at the ballot box. Above any policy disagreement, Democratic voters report that nothing matters more than finding a candidate who can beat Trump.

Their first round of debates is finished, but the real struggle is just beginning for most of the candidates.

All will work aggressively to leverage their debate performance and the related media attention to their advantage in the coming days. There is a real sense of urgency for more than a dozen candidates who fear they may not reach donor and polling thresholds to qualify for subsequent debates.

Should they fail to qualify, and many will fail, this week’s debates may have marked the high point for their personal presidential ambitions.

(AP)