Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE is ready to scrap.

The former vice president is firing back at his rivals and vowing to be more aggressive at the second presidential debates after weeks of sustained attacks against his civil rights record left his supporters frustrated and worried about his passive approach.

The tipping point, according to allies and campaign strategists, came on Wednesday at a NAACP presidential candidate forum, where Sen. Cory Booker Cory Anthony Booker3 reasons why Biden is misreading the politics of court packing Bipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility MORE (D-N.J.) accused Biden of being the “architect of mass incarceration” for supporting a 1994 crime bill.

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“You can't be called the architect of mass incarceration and remain quiet,” a Biden ally said. “That's cruel and personal. That goes against his entire career. You can't let people say bullshit and not respond to it.”

“The gloves are off,” the ally added. “At this point, you have to punch back when someone attacks your record. People want to see him throw a punch. The president is certainly going to come at him hard, so why not start now?”

The arrival of Fighter Joe comes as a relief to Biden’s supporters and sets the stage for a potentially brutal showdown next week in Detroit, where Biden, Booker and Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (Calif.) will share the same debate stage.

Harris catapulted into the top tier of candidates after the first debates, when she attacked Biden for opposing a decades-old federal busing program aimed at integrating schools and described his remarks about finding common ground with segregationist senators as “hurtful” to black people.

At the time, Biden avoided directly challenging Harris.

“I’m not going to be as polite this time,” Biden told donors at a fundraiser in Detroit on Wednesday.

Biden’s campaign is also boiling with anger at Booker. On Wednesday, the Biden campaign called Booker out by name for the first time and questioned his own record on civil rights.

Biden’s deputy campaign manager, Kate Bedingfield, said Booker “has some hard questions to answer about his role in the criminal justice system,” pointing to his promise as mayor of Newark more than a decade ago to implement a “zero tolerance policy for minor infractions.”

Bedingfield also accused Booker of “running a police department that was such a civil rights nightmare that the U.S. Department of Justice intervened.”

Meanwhile, Biden has signaled that he may take a shot at Harris’s record as California attorney general, perhaps accusing her of policies that led to the incarceration of racial minorities. Biden started down that path at the first debate, noting that he pursued a career as a public defender while she chose to become a prosecutor, but it was not a line of attack that he vigorously pursued.

“If [Harris and Booker] want to argue about the past, I can do that. I got a past I’m proud of,” Biden said Wednesday. “They got a past that’s not quite so good.”

Harris’s allies say they’re spoiling for the fight, an indication that the bad blood flowing between the two camps might become one of the defining developments of the Democratic primary race.

“I’m glad Joe Biden is going to be there this time and may be sharper,” said Melissa Watson, the Berkeley County chairwoman for the Democratic Party and a Harris supporter.

Watson expressed frustration with Biden’s remarks at the Wednesday fundraiser in which he vented at Harris for attacking him after he gave the keynote address at a convention where the California Democratic Party officially endorsed her for state attorney general.

“There’s an air of entitlement in all of his comments,” Watson said. “He’s saying, how dare she question him about his past. And he says he did her a favor, so that means she has no right to question him during a presidential primary? That’s crazy. They’re running for the highest office in the land.”

The focus on civil rights and the racially charged attacks flying between the candidates underscores the fierce battle for support from black voters in the Democratic primary.

Biden has slipped a little bit in the polls since the first debate, but he has maintained his standing as the clear front-runner in the race in part because of his enduring support from African Americans.

A Monmouth University survey released Thursday found Biden with a commanding lead in South Carolina, a critical early-voting state where black voters make up about 60 percent of the Democratic primary electorate.

Biden has 39 percent support overall in South Carolina, with Harris running a distant second place at 12 percent. The former vice president has 51 percent support from black voters in the state, followed by Harris, at 12 percent.

“Despite some supposed missteps on the issue of race, Biden maintains widespread support [among black voters],” said Monmouth University polling director Patrick Murray.

But Biden supporters know that support could evaporate with another shaky debate performance next week.

“I’m glad he’s finally pushing back, it should plug the leak, but he still needs to pull this off in prime time with both Harris and Booker flanking him on the dais,” said one Democratic strategist who supports Biden. “Make no mistake — another poor performance and this might be over for him. He doesn’t have the luxury of stacking bad debates on top of one another, especially with this many people coming after him.”

Biden was initially cautious about picking fights with Democrats, the ally said, because he “didn't want to contribute to a narrative that the president can use in a general election.”

But on the same note, “these are people who have come to him for advice, and have said what a great public servant he's been, and they're now attacking his record.”

The ally said the campaign is prepared for other campaigns to join the attacks.

“They see Harris had her moment and achieved what she wanted to achieve, and Booker is trying to have his moment, so why not?” the ally said.

“I think the message sent to him lately is that people want a uniter but they also want a fighter. He can be both. And when he needs to fight there's nothing he won't do.”

Biden spokesperson Andrew Bates said he’ll be ready for whatever his rivals throw at him.

“He's proud of his accomplishments, and many of his opponents were until a sudden, recent about-face,” Bates said. “We're not going to let anyone — whether Democrat or Republican — distort or misrepresent his record.”