The alarming thing about last night’s exchange with Kamala Harris over busing is not that Biden lost it but that he lost it even though it was totally predictable — so much so that I almost predicted it in the live thread published an hour earlier. I thought she’d come after him for his remarks about civility with segregationists in the Senate and for his work on the crime bill 25 years ago. In the end she chose busing instead of the crime bill, probably in part because busing gave her a way to introduce her own biography to viewers who were seeing her for the first time and partly because she’s saving the crime bill for a future debate when more people are watching. But either way, she was destined to hit him hard on racial issues. She needs to rupture his strong support with black voters as a predicate to winning over those voters herself. If she can’t she’s at risk of flaming out of the race early, especially if she disappoints in South Carolina.

Last night ended up being a twofer or even a three-fer for her. Not only did she throw light on one of Biden’s sins against racial wokeness, she demonstrated that she’s “tough” enough to take it to Trump on the debate stage if she’s the nominee. (Relatedly, Biden proved that he might not be equal to the task. How do you fail to duck a punch that you should have seen coming from a mile away, asks David Frum?) And she may have proved to black viewers watching over the course of two hours that she really is a serious threat to win the nomination. Obama didn’t start piling up black support against Hillary in 2008 until he began rising in the polls and ultimately won Iowa. To that point, many had stuck with Clinton in the belief that a major party would simply never nominate a black candidate for president. Once that perception changed, Obama took off. Harris might experience a similar surge if black voters, and really all Democratic voters, become convinced that she’s not only the most skillful debater in the field but also potentially the strongest opponent for Trump. If Biden begins to lose “electability” points to her, he may be done in a flash.

I’m skeptical that he will. The conventional wisdom on Twitter last night was that Harris had gutted him like a fish and left him to die but the Twitter conventional wisdom is almost always garbage, so much so that I’m tempted to bet that Biden will suffer no meaningful damage in the polls just because the Twitterati are convinced that he will. Early data is trickling in this afternoon, though, and the verdict is … mixed. The bad news for Uncle Joe comes from FiveThirtyEight, which is partnering with Morning Consult in polling likely Dem voters before and after the debates. Results: Hoo boy.

Biden was destined to lose some of his pre-debate support just because part of that support is due purely to name recognition. A few viewers who were supporting him due to sheer familiarity were sure to tune into the debates, size up the candidates, and find someone who catches their fancy. But 10 points is a big decline. And if you play around with FiveThirtyEight’s widget, you’ll find that a lot of that support seems to have gone to Harris herself. Before the debates she stood at 7.9 percent. Now she stands at 16.6 percent, in third place overall and less than a point behind Bernie Sanders for second. That’ll be a major shake-up if other polls confirm it next week. And if that support is coming mainly from black voters, it’s an ominous sign for Biden’s ability to maintain his grip on that group.

But there’s good news for him too. His favorable rating among Dems barely budged in FiveThirtyEight’s data, dropping less than a point over the course of the two debate nights. He’s still nearly 10 points higher than Harris herself in that metric. Also, New York magazine observed a large focus group of Democratic voters after the debates and found that Biden’s supposedly disastrous exchange with Harris wasn’t so disastrous:

• The biggest real-time polarization between the demographic groups over both debate nights came during Biden and Harris’s exchange on busing. “They were dramatically apart: African-Americans were responding fairly strongly, and others were not, to the debate on busing,” said Greenberg. “There was a [positive] reaction among African-Americans in support of what Harris was saying,” he explained, noting that college-educated women also backed her in the moment as she criticized the former-vice president’s past position. “But when [Biden] came back with what he was for, there was significant African-American support” for him, as well.

• By the time the first night’s debate was finished, Warren, Booker, and Julián Castro had all eaten into Biden’s overall support, particularly among African-American and Latino voters. But even though he was not on the stage, Biden’s support level actually rose among the non-college-educated white women. And, said Greenberg, “He still has an Obama base that’s there. Erosion should be part of the story, but we should not underestimate that coalition.” Indeed, on the second night, Biden earned both African-American and Latino support when he defended Obamacare, and his overall approval rose after he was done debating. “We’re seeing in the field, but you could also see it tonight, how enduring Biden’s support was, even with being attacked from all sides,” said Weingarten. “There is something about him being vice-president.”

Harris’s share of black voters rose “significantly,” according to Greenberg — but Biden’s approval among black voters rose as well. There’s obviously another clash between them, probably multiple clashes, to come on racial issues. The irony of last night’s killer exchange was that the balance of public opinion on busing has always been strongly on Biden’s side. Harris doubtless knows that and chose to ignore it, recognizing rightly that the path to the nomination (certainly her path to it) lies in consolidating black voters. Someone on Sleepy Joe’s campaign had better rouse him and convince him to be more assertive in touting his civil rights credentials next time, starting with the fact that he was handpicked by the first black president to be VP, or his candidacy’s going to collapse.

He and his team are worried. He tried cleaning up the busing comments during an appearance today, as you’ll see below, then beamed out a statement to his supporters. News is breaking this afternoon that he’s lost a major fundraiser (although supposedly that decision was made before the debates) and allies are whispering to the media that he knows he had a bad night and needs to do better. Stay tuned.