Kamala Harris and Elizabeth Warren making big gains. Photo: Joe Raedle/Getty Images

One of the hallmarks of the first stage of the 2020 Democratic nominating contest was the stability at the top of the polls. For months, Joe Biden and Bernie Sanders dominated the field nationally as well as in most early-state surveys. Other candidates waxed and waned in support and in their relationship to each other but didn’t really challenge the septuagenarian Big Boys.

That started to change in June, at least with respect to Bernie Sanders, whose lead over a slowly surging Elizabeth Warren generally faded and occasionally disappeared or was reversed. But Joe Biden seemed impervious to the political tempests, even after major adverse news stories about his past record or the occasional gaffe.

Now there is some evidence the first round of Democratic debates have created serious turbulence in the field. A new CNN/SSRS national poll taken entirely after the debates shows both Warren (15 percent) and Kamala Harris (17 percent) running ahead of Sanders (14 percent) with Biden still in the lead but losing altitude (22 percent). As compared to the last CNN survey a month ago, Biden has lost ten points and Sanders four points, while Harris has gained nine points and Warren eight points. No one else held more than 5 percent of the vote (Pete Buttigieg was in fifth place with 4 percent).

Given what happened during last Thursday night’s debate, it may be even more significant that CNN showed Harris leaping from 4 percent to 19 percent among nonwhite voters since the last poll, while Biden dropped from 30 percent to 25 percent in that same demographic. This is precisely the sort of switchover in minority voting that Kamala Harris’s entire strategy depends on. She may actually have gained some of that nonwhite support from Sanders, who dropped from 20 percent among those voters to 13 percent in the latest survey. Warren had a more modest improvement from 8 percent to 13 percent among nonwhite voters.

According to an analysis of the results from CNN, among African-American voters alone, Biden now leads Harris 36-24, with other candidates trailing well behind.

The other publicly available post-debate numbers come from the Morning Consult tracking poll (a methodology that often shows more stable results over time). They were also harvested a couple of days earlier, which means they probably picked up less of the post-debate spin than CNN did. This survey showed Biden losing five points since June 23 and now holding 33 percent of the vote; Sanders a steady second at 19 percent; and Harris and Warren tied at 12 percent, which represented a doubling of Harris’s support since June 23. Morning Consult had Pete Buttigieg down slightly to 6 percent.

CNN separately asked about debate performances, and the numbers confirmed Kamala Harris’s big night, while casting doubt on the impact of the generally strong impressions made on many observers by Pete Buttigieg, Cory Booker, and Julián Castro:

Among those who watched or followed news coverage about them, 41% say Harris did the best job in the debates, well ahead of the 13% who say Warren had the best performance and 10% who said Biden did. Among those who say they watched all or most of at least one night of debates, Harris’ showing is even stronger: 46% say she did the best job, 19% Warren, 8% Biden and 5% each named South Bend, Indiana, Mayor Pete Buttigieg and former secretary of Housing and Urban Development Julian Castro.

All in all, these results show that candidate preferences are significantly less stable than they appeared for a good while, and that the theory holding that Democratic voters are terrified to nominate another woman to run against Trump is less credible than originally thought. Next month’s debates, of course, could unsettle our understanding of the race, too. And structural factors (including the strong Sanders and Warren organizations and Pete Buttigieg’s enormous second-quarter fundraising haul) are worth keeping in mind. But at present, early leaders Biden and Sanders are trending in the wrong direction.