(CNN) - Program notes: (This is the 15th edition of our power rankings of Democrats most likely to get their party's presidential nomination in 2020.)
The big story of recent vintage in the 2020 presidential race is the struggle of frontrunner Joe Biden. And rightly so! The former vice president has come back to the pack after a searing start to the race -- brought low(ish) by a seeming praise for a segregationist senator and a mediocre performance in the first debate.
All true! But the Biden storyline has overshadowed another important development in the 2020 Democratic campaign: A top tier has emerged!
That lead pack has four candidates: Biden, California Sen. Kamala Harris, Massachusetts Sen. Elizabeth Warren and Vermont Sen. Bernie Sanders. Biden remains the nominal frontrunner of the quartet, but Harris and Warren are chasing at his heels while Sanders appears to be clinging on to stay with the frontrunners.
The distance between those top four and the rest of the 200 -- rough estimate! -- other people running for the Democratic nomination, from an organizational and polling perspective, is real and significant.
South Bend Mayor Pete Buttigieg, who is currently on the outside looking in at the Big 4, has the best chance of breaking into the top tier at the moment, due to the almost $25 million he raised in the second quarter.
Below, the 10 candidates with the best chance of winning the nomination when voters start voting.
10. Andrew Yang: You would be forgiven if you asked whether this businessman actually took part in the first Democratic debates. Yang's performance was utterly forgettable, as he spoke for the least amount of time on the night he debated. More worrisome for Yang is that while he's almost certain to make the CNN debate at the end of this month, he's in real danger of not making the September debates. Yang has hit the donor threshold, but hasn't hit the necessary 2% in any qualifying poll. (Previous ranking: 9)
9. Julián Castro: The San Antonio mayor needed a moment to stand out from the crowd -- and he got one in the first debate. Castro was thoughtful, forceful and, aside from Warren, the class of the stage of the first night of the first debate. (He absolutely drubbed fellow Texan Beto O'Rourke in an exchange on immigration.) The question now becomes whether the bump he should get is enough to catapult him into real contention. So far, Castro's polling movement has been minimal. (Previous ranking: 10)
8. Amy Klobuchar: The senior senator from Minnesota remains steady in our rankings. She didn't make much noise in the June debates, and her polling remains mostly lackluster. But in a way, the debates were good for her. Right now, three of the top four candidates in our rankings have very liberal voting records. The only one who doesn't (Biden) has seen his polling falter. If Biden collapses, a moderate like Klobuchar could be in a position to run as the moderate alternative to the other liberal campaigns. (Previous ranking: 8)
7. Beto O'Rourke: You know when you are really looking forward to a vacation? Like, for months you look at the pictures of the hotel and plan your days? And then you get there and the hotel is kind of run down and the weather stinks? That's O'Rourke's presidential campaign so far. (Previous ranking: 6)
6. Cory Booker: If it weren't for Harris stealing his thunder on night two, the junior senator from New Jersey might be remembered for having a strong debate on night one. Further, Booker has the fundamentals of a strong candidate. His record is liberal though not overly so, which could be the sweet spot in this primary. Booker's primary preference polling is not great, though he still has pretty good favorable ratings. Booker's the type of candidate that is probably one debate moment away from jumping up considerably in the polls. (Previous ranking: 7)
5. Pete Buttigieg: We knew that Buttigieg was going to raise a ton of money between April 1 and June 30 since he was the "it" candidate in the race for much of that time. But $25 million??? More than Biden, Sanders, Warren and Harris? That's a truly stunning number for a guy no one had heard of six months ago. Buttigieg's poll numbers have sunk a bit from his peak in the high single-digits (or low double-digits), but that sort of fundraising should solve a lot of those problems. (Previous ranking: 5)
4. Bernie Sanders: The junior senator for Vermont was already competing with Warren for second place in the polls pre-debate. Now, it's a three-way tie for second place nationally among Harris, Sanders and Warren. That's certainly good enough to remain a top four candidate, and his candidacy is far from dead. Remember though, Sanders has higher name identification than Harris or Warren. His polling in Iowa puts him in a clear fourth. Plus, Sanders has fallen well behind Harris in the endorsement primary and even got beat in fundraising by Warren last quarter. (Previous ranking: 3)
3. Elizabeth Warren: Warren remains in a very good spot in this race. She was terrific in the first debate and the $19 million she brought in during the second quarter is proof of her momentum in the contest. Warren's move past Sanders -- especially among the most liberal voters -- is a very big deal especially if she can keep it up. (Previous ranking: 2)
2. Kamala Harris: What a difference a debate makes. The junior senator from California had frequently topped our power rankings for much of 2018 but had fallen behind before the first debate. But after her debate showdown with Biden, Harris has seen her polling boom. Her support has jumped with African-Americans. Harris is also the only candidate besides Biden who has gotten a significant number of endorsements outside her home state. The big question is whether Harris can keep it up as the spotlight shines on her. She's struggled before, and continues to struggle on accusations of flip-flopping on issues such as busing and health care. (Previous ranking: 4)
1. Joe Biden: The former VP isn't in as strong a spot as he was even the last time we did these ratings a few weeks ago. He looked out of touch during the first debate and continues to deal with the fallout from Harris' attack -- and his botched response -- on segregated busing. Biden is still the best-known candidate in the field and remains generally well-liked by the voters he needs to woo. But he has fallen very quickly from the heights he reached early in the contest. (Previous ranking: 1)