Their relative strength may vary, but Biden, Warren, and Sanders are jockeying for position. Photo: Getty Images

This week we will hear a lot of talk about which 10 or 11 or 13 of the 2020 Democratic presidential candidates have been “winnowed” from the field by the DNC’s debate qualification requirements (the deadline for qualifying polls or donor verification for the September round of debates is Wednesday, August 28). But beneath the surface, a more subtle but important type of winnowing may be underway, as three strong candidates (Joe Biden, Bernie Sanders, and Elizabeth Warren) jockey for position while everyone else struggles for oxygen.

A new national survey from the well-regarded Monmouth University outfit shows big-time churn among the Big Three. Compared to Monmouth’s last poll in June, Joe Biden has lost 13 points (from 32 percent to 19 percent), while Bernie Sanders has gained 6 points (from 14 percent to 20 percent) and Elizabeth Warren has gained 5 points (from 15 percent to 20 percent). Together the three candidates had 61 percent of the vote in June and have 59 percent now. The only other candidate who gained more than a single point since that June poll was Cory Booker, who rose from 2 percent to 4 percent. Yes, the timing of the Monmouth polls means that it did not capture the brief surge in support for Kamala Harris after the first round of Democratic debates. But Monmouth now has the Californian at 8 percent, just above her national polling average (7.5 percent) at RealClearPolitics. No other candidate has even threatened double digits nationally this calendar year.

Perhaps most strikingly, the virtual collapse of Biden’s support between the June and August Monmouth surveys has not materially benefited any of the moderates-in-waiting who have been, well, biding their time in hopes that the longtime front-runner would stumble. Among self-identified moderate-to-conservative Democrats, Biden still leads with 22 percent, but Sanders is second at 20 percent, and Warren third at 16 percent. Harris is a poor fourth at 5 percent, while Pete Buttigieg is at 4 percent, and Amy Klobuchar at 2 percent. Similarly, the nonwhite candidates who expected to make big gains if Biden slipped aren’t benefiting much, as support is swapped around between the Big Three. Among nonwhite Democrats, Sanders now leads with 22 percent, while Biden is second at 19 percent, and Warren is third at 14 percent. Kamala Harris, who can claim both African-American and Asian-American identity, is fourth at 9 percent; Asian-American Andrew Yang is at 5 percent, while Latino Julián Castro is at 3 percent.

Yes, this is just one national poll, but the domination by the Big Three in virtually every demographic category is typical. Fox News polling has showed Biden, Warren, and Sanders together holding 61 percent of the vote in May, 60 percent in July and 61 percent in August. In the latest Fox poll the three leading white candidates hog 60 percent of the nonwhite vote as well, with Harris a poor fourth at 7 percent. In a mid-August CNN survey the Big Three have a combined 58 percent, with Buttigieg and Harris tied for third at 5 percent.

Nor does the picture change that much in the early states. Using RealClearPolitics polling averages, the Big Three have 58 percent in Iowa; 55 percent in New Hampshire; 61 percent in Nevada and 65 percent in South Carolina. You have to get to Kamala Harris’s home turf of California to find a relatively early state where anyone outside the Big Three actually ranks in the top three, but even there, the latest poll has her running fourth.

Things can obviously change between now and the time voters begin voting; someone could theoretically replicate Harris’s breakout performance in the first debates (including Harris herself), but it may be telling that her bounce didn’t last. 2020 could wind up resembling 2008, when there were eight candidates (including a veteran senator named Joe Biden), but only three made much of a mark in Iowa, and after John Edwards failed to win there, it was basically a two-candidate race between Barack Obama and Hillary Clinton. There may simply be too many candidates for voters to focus on the entire field. Or quite possibly, in these three white septuagenarians, Democrats could find a sufficient range of options to satisfy their tastes, and their varying thoughts about how to beat Donald Trump.