"Everybody is talking about how bad I am on these issues", Mr Bidensaid, referring to his record on race.
In turn, Harris was attacked for the healthcare plans she rolled out earlier in the week, which will be phased in over ten years, well past her second term, should she win the Democratic nomination and a first term at the White House - a long shot considering she is running about fourth in the nomination race behind Biden, Sanders, and Elizabeth Warren.
"I'm concerned about this record of senator Harris".
But at the same time, polls show Mr Biden has far more support from minority voters than his challengers, especially in the crucial early voting state of SC.
"I'll be honest with you, I'm drawing a blank on what he's accomplished", one debate attendee said, while another added, "I don't know of a specific accomplishment of his".
"I have guts enough to say his plan doesn't make sense", Biden said of Castro. Harris was also on the defensive at times, failing to repeat her dominant performance in Miami.
Democratic presidential candidates Sen. When Sen. Michael F. Bennet (Colo.) pointed out that her plan would make employer-sponsored insurance illegal, Harris denied it - only to later admit to CNN's Anderson Cooper that, well, yes, it would.
In an exchange with Julian Castro, the former housing secretary under Obama, Biden criticized Castro's plan to decriminalize illegal border crossings.
"Senator Biden, your plan will keep and allow insurance companies to remain with status quo, doing business as usual, and that's going to be about jacking up co-pays, jacking up deductibles", Ms Harris said. That didn't matter so much when Harris was one of many hopefuls and could simply deliver her focus-grouped talking points.
The alleged remark, which Trump was never confirmed to have made, received a widespread backlash, particularly from Democratic lawmakers.
Booker signaled in the weeks leading up the debate that he was going to take Biden to task for his stewardship of a 1994 crime bill that exacerbated mass incarceration in communities of color. Later, she tried to deflect criticism of her plan's enormous cost with a non sequitur about expensive prescription drugs, as if it were impossible to control drug prices without nationalizing the entire USA health-care system.
"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 a position to nominate" Mr Biden to become vice president, she said.
Laughable as it may seem, Biden is the not-crazy one in the Democrat field.
"Especially when people are at zero or 1% or whatever (Gabbard) might be at", Harris added.
Biden countered with criticism of her record as California's attorney general, claiming Los Angeles and San Francisco schools were two of the most segregated school districts under her watch. Harris warded off the attack, later trashing Gabbard for being a supporter of Syrian president Bashar Al Assad and ridiculing her low numbers in the polling that showed her (Harris) in the lead pack.