Former Vice President Joe Biden may be the frontrunner, but he faces significant questions over his record on racial issues and criminal justice at the second Democrat presidential debate.

Biden, who has been warning rivals that he will not refrain from punching back if criticized, is likely to face attack from two 0f his most high-profile challengers, Sens. Kamala Harris (D-CA) and Cory Booker (D-NJ), over the issues during Wednesday’s debate.

The most imminent danger comes from Harris, who at the first debate hammered Biden over his praise for two segregationist Democrats. Biden had invoked the two men, Sens. James Eastland (D-MS) and Herman Talmadge (D-GA), repeatedly on the campaign trail while touting his ability to forge “consensus” in Congress.

“I agree with you when you commit yourself to the importance of finding common ground,” Harris said, “but I also believe … it was hurtful to hear you talk about the reputations of two United States senators who built their reputations and career on the segregation of race in this country.”

Given the short amount of time provided by the debate’s moderators, the California Democrat was quick to point out that both Talmadge and Eastland were allies in Biden’s crusade against busing to integrate public schools.

“It was not only that, but you also worked with them to oppose busing,” Harris said. “There was a little girl in California who was part of the second class to integrate her public schools and she was bussed to school every day. That little girl was me. So I will tell you that on this subject, it cannot be an intellectual debate. … We have to take it seriously.”

The attack left Biden reeling to respond. The former vice president accused Harris of mischaracterizing his record. Instead of offering proof, however, the 76-year-old frontrunner only jumbled his position on busing and falsely claimed to have never praised racists.

After the altercation, Harris’s polling numbers steadily climbed, but have stalled as of late. Biden’s level of support, on the other hand, dropped immediately after the debate, only to rebound in recent weeks. Compounding the problem for Biden — and perhaps making him an even more attractive target for Harris — is that he has struggled to explain his position on busing in an adequate way to pacify social justice activists, who are an increasingly loud contingent within the Democrat base.

Booker, meanwhile, is likely to assail Biden over his decades-long support for tough-on-crime initiatives. The attacks could potentially be fatal to Biden’s newborn efforts to shed his law and order image by embracing criminal justice reform.

Earlier this month, under criticism for having authored the 1994 crime bill, Biden pledged to cut incarceration by more than 50 percent if elected president. He followed up the promise by releasing a criminal justice reform proposal centered around eliminating mandatory minimum sentences and ending prison time for some drug offenses.

Booker, who has championed such efforts since joining the Senate in 2013, appears not to be buying the makeover. The New Jersey Democrat has not only lambasted Biden’s plan to curtail mass incarceration as falling “short of the transformative change” needed, but also questioned if it was appropriate for him to lead such a charge in the first place.

“Joe Biden had more than 40 years to get this right,” Booker said last week. “The proud architect of a failed system is not the right person to fix it.”

Along similar lines, Booker is likely to target Biden’s freshly minted reversal on the death penalty, after decades of supporting its expansion, at the debate on Wednesday. The strike could be significant, especially as the Department of Justice has just announced it will resume executions after nearly a 20-year reprieve. Four of the five men newly slated for execution are on death row because of provisions within the 1994 crime bill that Biden authored and fought to pass.

Biden’s team, seemingly aware of the danger posed by Booker and Harris, has already launched an effort to discredit not only their attacks, but them as well.

Since the first debate, Biden and his mostly-male surrogates have attempted to paint Harris as overly ambitious and ungrateful for the support the former vice president has given her in the past.

“It’s not right, it’s distressing. It shows a lack of integrity: win at any cost,” Dick Harpootlian, the Biden campaign’s surrogate in South Carolina, told Politico when discussing Harris’s busing rebuke at the first debate. “Why is she taking that shot when Joe Biden and his son did everything they could to help her? It was more of a comment about her than it was about Joe Biden.”

The frontrunner himself, although initially refusing to make it personal because of Harris’s friendship with his late-son Beau Biden, has echoed similar sentiments recently.

“I’m not going to be as polite this time,” Biden warned last week. “Because this is the same person who asked me to come to California and nominate her in her convention.”

The former vice president and his team have followed a different course with Booker, choosing instead to paint the senator as hypocrite on criminal justice issues. Last week, shortly after the New Jersey Democrat rebuked the frontrunner as the “architect of mass incarceration,” Biden’s campaign punched back saying if anyone had “hard questions to answer” over their role in expanding the prison population it was Booker.

Kate Bedingfield, the former vice president’s deputy campaign manager, sent an email to the press denoting several decisions Booker took as mayor of Newark, New Jersey, that appeared to cast doubt on his commitment to criminal justice reform. Citing Booker’s support for zero tolerance when it came to minor criminal offenses and the alleged “civil rights abuses” of his police department, Bedingfield argued the New Jersey Democrat had done more to further mass incarceration than Biden.

“Since next week’s debate format will give Senator Booker twice as much time to make his attacks than it allows Vice President Biden to respond to them, we thought we would begin to respond now,” she said.