• Sen. Kamala Harris and former Vice President Joe Biden debated over the former Vice President’s oppositions to federally-mandated integrated busing. It didn’t go well for Biden.
  • Harris’ approach has three major benefits according to INSIDER’s ongoing polling, which focuses on overlapping constituencies among the candidates.
  • First, Biden’s supporters have been less likely than typical Democrats to be satisfied with non-Biden contenders. By threatening his perception as the sole acceptable candidate, Harris can erode his support.
  • Second, 67% of Harris supporters would also be satisfied with Biden as nominee. This was her chance to lock them down and settle that debate.
  • Third, Harris already leads the presidential campaign newbies on electability in the general. This can only improve that.

California Sen. Kamala Harris had the most compelling moment of the second debate when she took former Vice President Joe Biden to task over his historic opposition to federally mandated busing in his early years as a senator.

“I do not believe you are a racist, and I agree with you when you commit yourself to the importance of finding common ground,” said Sen. Harris, “but it’s personal and 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.”

She then proceeded to recount how Biden’s opposition personally impacted her, and the former Vice President struggled to recover.

Biden has long cast his experience in the Senate and bona fides as a politician willing to cross the aisle as a considerable asset in his pursuit of the presidency, but one side effect of that kind of resume is that it makes attacks like this so biting.

Read more: Kamala Harris was the breakout star of the second night of Democratic debates, outperforming frontrunners Biden and Sanders

Harris' knock on Biden was compelling because it was the kind of moment from a chaotic debate that stands out. We'll see over the next few days and weeks whether that line of attack is persuasive to voters and whether it has a meaningful dent on Biden's soaring polls, but there are three reasons it landed so well and could sting for the former Vice President down the line.

Former Vice President and 2020 Democratic presidential candidate Joe Biden addresses patrons and media during a visit to the Stonewall Inn, Tuesday, June 18, 2019, in New York. Biden paid a visit to the Stonewall Inn ahead of the 50th anniversary of an uprising that helped spark the gay rights movement. (AP Photo/Bebeto Matthews)

Foto: Joe Biden.sourceAP Photo/Bebeto Matthews

It threatens Biden's key asset, a perception only he alone can go toe-to-toe with President Trump in the general

INSIDER has been conducting recurring polls on SurveyMonkey Audience over the course of the election. Lots of pollsters are focused on the key question of the primary, namely who respondents would vote for if the primary were held today. We're not asking that question. We want to know which of the (many) candidates our poll respondents would be satisfied with as Democratic nominee. We're interested in overlapping constituencies, namely which candidates are consolidating which lanes, and who is squabbling over the same voter.

READ MORE: How the INSIDER 2020 Democratic primary tracker works

Biden has been a bit of an enigma so far this primary. If you look at, say, Sen. Cory Booker, I can tell you that the Democratic voters who'd be satisfied with Booker are also disproportionately satisfied with Sen. Kamala Harris, Sen. Elizabeth Warren, and Rep. Beto O'Rourke, and I can tell you his supporters are less drawn to Gov. Hickenlooper and Mayor Pete Buttigieg than the typical Democrat, our polling shows.

But Biden? For every single candidate in the race, people who'd be satisfied with Biden as nominee are less likely than the typical Democratic respondent to like each and every other candidate. Every non-Biden candidate is in the red.

While 40% of Democrats like Cory Booker, only 30% of Biden supporters do. When 50% of Democrats like Harris, only 39% of Biden supporters do. When 52% of Democrats like Pete Buttigieg, only 27% of Biden supporters do. They're picky. You see something slightly similar with Sen. Bernie Sanders fans, but even Sanders fans tend to like Sen. Elizabeth Warren more than the typical Democrat.

In reality, those two have both run national presidential campaigns before, which Kamala Harris and the other contenders have not. So Democrats who want a sure thing, a guaranteed shot, may be inclined to play it safe and prefer the known quantity and not back a candidate who can't go toe-to-toe with the sitting president.

By not only having that debate with Biden but also by, in the popular perception, beating him, that threatens the key perception that Biden alone among the contenders has the capacity to hang tough in that kind of circumstance. And should Biden look mortal, those supporters who are unwilling to consider other candidates now may begin to consider their new alternatives.

Kamala Harris/Joe Biden

Foto: sourceScreenshot via MSNBC

Lots of people who'd be satisfied with Harris as nominee would also be satisfied with Biden. This may lock them down.

This stage in the process you have lots of Democratic voters who are amenable to a wide swath of candidates. It's months before even the Iowans have to make up their minds. So while the media tends to fall back on reductions, perhaps contrasting the "Biden wing" of the Democratic party with the "Bernie wing" of the party, in reality the overlap is considerable. Fully 49% of Democratic voters who'd be satisfied with Biden as the Democratic nominee would also be satisfied with Sen. Bernie Sanders as the Democratic nominee, our polling shows!

Clearly there is opposition: 25% of those satisfied with Biden said they would not be satisfied with Sanders, which is very high, but the point stands that today there remains lots of overlap.

For Harris, Biden remains the single largest threat in that department. Biden, by virtue of being the frontrunner, is the single largest threat for most candidates. But for Harris the numbers have to be troubling, especially for a candidate who is in the top four.

Based on our data, 67% - fully two thirds - of respondents satisfied with Sen. Harris as nominee would also be satisfied with Biden as nominee. That's not so high in the opposite direction, largely because of that first effect I talked about, Biden's perception among voters.

By striking true at a key weak point of Biden's, I imagine that Harris may have been specifically attempting to appeal to those voters. In those 10 polls since March, we got responses from 4,324 people who said they were registered to vote and who'd participate in their state's Democratic primary or caucus. Fully 868 of those people, a fifth of the set, would be satisfied with both Harris and Biden.

That incisive critique of the former Vice President was a solid bid to get that fifth to make up their minds. Whether it's effective remains to be seen, but it's really sensible for Harris to try to lock down those fans.

In this June 17, 2019, photo, Democratic presidential candidate Sen. Kamala Harris, D-Calif., speaks at the Poor People's Moral Action Congress presidential forum in Washington. Harris is stepping up her outreach to the black community as she campaigns for the Democratic presidential nomination. (AP Photo/Susan Walsh)

Foto: In this June 17, 2019, photo, Democratic presidential candidate Sen. Kamala Harris, D-Calif., speaks at the Poor People's Moral Action Congress presidential forum in Washington. Harris is stepping up her outreach to the black community as she campaigns for the Democratic presidential nomination. (AP Photo/Susan Walsh)sourceAssociated Press

Harris already enjoys a higher-than-typical perception she could beat Trump in the general election. This underscores that advantage.

Harris is unquestionably in the top tier of this race, and her advantages above the rest of the competition can't be understated. We'll regularly ask respondents to our poll how they think the candidates they're aware of would do in a general election against Donald Trump. For a given candidate that a respondent is aware of, 31% of Democratic primary voters say they'd win, 27% say they'd lose and the rest are uncertain.

Read more: Democratic voters have high expectations for the frontrunners at the first debates of the 2020 campaign, according to a new poll

For Biden, the perception among Democrats - in keeping with the perceptions we mentioned earlier - is more often that he'd win against Trump than he'd lose. 70% of the time someone was aware of Biden, they said he'd probably win, and 14% they said he'd probably lose. Similarly for Sanders, 48% of the time a Democrat knew him they said he'd win, 23% of the time they said he'd lose.

Only 4 other Democrats do better than that 31% win/27% lose generic performance.

  • O'Rourke and Buttigieg barely beat that generic performance, winning about a third of the time a Democratic respondent knew of them and losing about a quarter of the time.
  • Elizabeth Warren is said to likely win by 35% of those who are aware of her candidacy, but 31% said she'd lose to Trump, perhaps the nagging memory of early campaign mishaps.
  • For Kamala Harris, 38% of Democratic respondents aware of her campaign think she'd win, 7 points higher than the generic, and 25% think she'd lose, two points shy of the generic.
  • Only Harris can claim to be perceived as a stronger-than-typical candidate in the general at this time.

All that being said, this means that her successful confrontation with Biden has three potential electoral advantages.

First, it hits Biden where he's strong, as a candidate favored by Democrats who do not think the other contenders have a shot, and who for now haven't been keen to look beyond the known quantities.

Second, we'd estimate about a fifth of Democratic primary voters would be satisfied with both Biden and Harris, and by landing such a serious hit on the former veep, Harris could attempt to consolidate some of that overlap.

And third, Harris is already considered more electable than all of her other rivals who haven't already run for president. This cements her as a candidate on the same tier as Sanders and Biden when it comes to general election viability.

In short, in just a few brief minutes Harris may have neutralized her primary rival, snagged some of his support, and bolstered her own core advantage. We'll see if that goes anywhere, but not bad.