DETROIT — Sens. Cory Booker and Kamala Harris — the two black candidates in the crowded 2020 Democratic field — teamed up to prosecute former Vice President Joe Biden's record on health, race and criminal justice while others joined the pile on Wednesday during the second 2020 Democratic presidential debate.

All eyes were on Biden, the front-runner, who was a target of the nine other candidates on stage at the CNN-sponsored event here at the historic Fox Theatre.

But the former vice president, who was caught off guard in the last debate, came prepared this time to to defend himself — and go on offense against his rivals.

Right at the start, Biden attacked Harris' support for a single-payer health care system as too expensive, too slow to implement and too disruptive because it would take away Americans' private insurance and replace it with a government-run plan in 10 years.

And he dinged the California lawmaker for having a stance that was, until she released her plan this week, sometimes difficult to pin down.

"This idea is a bunch of malarkey," Biden said. "And to be very blunt and to be very straightforward, you can't beat President Trump with doubletalk on this plan."

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"Obamacare is working," Biden said, explaining he wants to build on the Affordable Care Act and offer a public option, instead of replacing it with Medicare for All.

Harris found herself in the uncomfortable position of having to defend a plan better associated with Bernie Sanders than herself, but was stronger on the counterpunch to Biden's.

"You're just simply inaccurate," she said. "Your plan does not cover everyone in America. By your own staff and your own definition, 10 million people — as many as 10 million people — will not have access to health care. And in 2019, in America, for a Democrat to be running for president with plan that does not cover everyone is without excuse."

Anticipating their rematch, Biden had earlier greeted Harris to the debate stage with a handshake and an appeal to his 54-year-old rival caught on an open microphone: "Go easy on me, kid."

Booker, the only other black candidate in the race, at first tried to rise above the fray — but then tore in Biden for sponsoring the 1994 crime bill.

The two had been sparing for weeks, so Biden called out Booker for doing "nothing" during his eight-year tenure as mayor of Newark, N.J., to "deal with the corrupt police department."

With a smile and laugh, Booker responded, "There's a saying in my community. You're dipping into the Kool-Aid, and you don't even know the flavor."

"If you want to compare records and, frankly, and I'm shocked that you do," Booker said, "there are right now people in prison for life for drug offenses because you stood up and used that phony 'tough on crime' rhetoric that destroyed a lot of communities like mine. ... I'm glad you evolved, but you offer no redemption to those people."

Harris jumped in to support Booker, saying that as the former district attorney of San Francisco and attorney general of California, she has spent her career "cleaning up the consequences of the bills that you passed when you were in the U.S. Senate for decades."

And she knocked Biden for touting his work with segregationist senators.

"Had those segregationists (had) their way, I would not be a member of the United States Senate, Cory Booker would not be a member of the United States Senate and Barack Obama would not have been in the position to nominate him to the title he now holds," Harris said.

But Harris has her own vulnerabilities on criminal justice in the post-Black Lives Matter era from her time as a prosecutor, which her rivals were quick to exploit and she struggled to effectively parry.

"The bottom line, Senator Harris, is when you were in a position to make a change in these people's lives you did not," Rep. Tulsi Gabbard of Hawaii said in a lengthy evisceration of Harris' record. "The people who suffered under your reign, you owe them an apology."

Colorado Sen. Michael Bennet took the opportunity to try to bring the issue of segregation into the modern era.

"This is the fourth debate that we have had and the second time that we have been debating what people did 50 years ago with busing — when our schools are as segregated today as they were 50 years ago," he said.

When the conversation came back around to Biden, he, as he often does, turned to former President Barack Obama to mount a defense.

"He chose me (for vice president) and he said it was the best decision he ever made," Biden said.

When the debate questions turned to immigration, Booker also used the Obama defense against Biden, pressing the former vice president on whether he advised his boss against deporting a record number of migrants.

"Mr. Vice President, you can't have it both ways. You invoke president Obama more than anybody else in this campaign. You can't do it when it's convenient," Booker said to cheers.

Biden said he would keep his advice to Obama private, before defending his former boss for protecting Dreamers — young people brought to the U.S. illegally as children — and trying to pass a comprehensive immigration reform plan.

"I think the president of the United States, Barack Obama, went out of his way to try to change the system," Biden said.

Former Housing Secretary Julián Castro touted his plan to decriminalize unauthorized border crossings, which prompted Biden to take a shot.

"His plan doesn't make any sense," Biden said, blaming Trump for "abusing" immigration laws but saying migrants still need to "wait in line."

Biden noted that he and Castro sat together in many meetings during their service in the Obama administration and Biden said, "I never heard him talk about any of this when he was (HUD) secretary."

But Castro stood his ground. "It looks like one of us has learned the lesson of the past, while the other of us has not," he said. "What we need are politicians that actually have some guts on this issue”

From there, it was open season on Biden.

Sen. Kirsten Gillibrand of New York — who joked that the first thing she would do in the White House would be to “Clorox the Oval Office" — went after him on gender.

She said Biden had written that women working outside the home would lead to the deterioration of the family, but the former vice president turned the attack around on the New York senator by noting that his wife has worked the entire time they’ve been married and that Gillibrand has praised Biden’s record on women in the past.

"I don’t know what's happened, except that you're now running for president,” Biden said, which seemed to leave Gillibrand a bit flummoxed.

Washington Gov. Jay Inslee, whose campaign is largely focused on climate change, said Biden's plan is "too little, too late." "Middle ground solutions like the vice president has proposed...are not going to save us," Inslee said.

A number of candidates on stage Wednesday were fighting for their political survival ahead of the fall, when the threshold to qualify for the next debate is expected to winnow the field.

One of those is New York City Mayor Bill de Blasio, who hectored Biden from the left throughout the debate and urged Democrats to go big.

"Donald Trump will call us socialists," de Blasio said. "Donald, you’re the real socialist. The problem is it’s socialism for the rich."

Meanwhile, Yang, the only real political outsider on the stage, used his closing argument to condemn the entire spectacle of American politics in the 21st Century.

"We're up here with makeup on our faces and our rehearsed attack lines, playing roles in this reality TV show," he said. "It's one reason why we elected a reality TV star as our president. We need to be laser-focused on solving the real challenges of today."