There have now been five national polls since the first Democratic presidential primary debate. Together, the surveys, conducted by ABC News/Washington Post, Quinnipiac, CNN, The Hill/Harris, and Politico/Morning Consult, show the debate has shaken up the race. The field has separated into three clearly definable tiers, all atop a large group at the bottom made up of candidates with virtually no support.

Within the first tier, Joe Biden, Bernie Sanders, Kamala Harris, and Elizabeth Warren, the leaders' positions are rapidly shifting. Since the debate, only one of the four, Harris, is up, while Biden, Sanders, and Warren are down.

On the day of the debate, Biden stood at 32% in the RealClearPolitics average of polls. Now, he is down four points, to 28%. That is the biggest drop of anyone in the field.

The second-place Sanders has experienced a much smaller decline, from 16.9% to 16%. But he is still closer to Biden than before because of Biden's big drop.

Harris has surged into third place, shooting up from 7% before the debate to 14.6% now. That is the biggest change, up or down, of all the candidates. There has been a lot of second-guessing after Harris' pre-planned attack of Biden over his opposition to 1970's-era forced busing. Busing was wildly unpopular and is widely viewed as a failed policy. How could Harris gain after pointing out that Biden was, in retrospect, right about busing? Well, she has — a lot.

Warren, who was comfortably in third place before the debate, is now in fourth place, down just a bit from 12.8% to 12.4%.

That's the first tier. After that, there is a big drop-off to a three-candidate second tier. In it are Pete Buttigieg (down from 6.6% to 4.8%) in fifth place; Beto O'Rourke (down from 3.3% to 2.4%) in sixth place, and Cory Booker (up ever so slightly from 2.3% to 2.4%) in seventh.

After that is a third tier of candidates, Julián Castro, Amy Klobuchar, Tulsi Gabbard, and Andrew Yang, who can muster 1% in the polls, but not much more. Castro, widely seen as having had a good debate, is up a bit, but the entire third tier is far, far back.

And then there is the large bottom group of candidates who are nowhere. Michael Bennet, Kirsten Gillibrand, Jay Inslee, Bill de Blasio, John Delaney, Steve Bullock, Tim Ryan, John Hickenlooper, and Marianne Williamson — they're all at 0.4% or less. They were at the bottom before the debate and they're at the bottom now.

The crowded lower ranks, 13 candidates below 2% support, has led to new calls for some to drop out. "I hope a whole lot of these folks will decide sooner rather than later to step aside," Democratic strategist Jim Manley told the Washington Examiner's Emily Larsen. "It's just a vanity project."

Comedian Bill Maher was a bit more blunt, naming ten candidates and telling them to "get the f--k out."

At some point, that's going to start happening. The next debate, conducted by CNN, is scheduled for July 30-31 in Detroit. Like the first debate, it will be a two-nighter to accommodate the large number of candidates. Maybe all 20 from the first debate will show up for the second. But certainly after that, the bottom of the bottom will increasingly face the question: Why are you still in?

