New York City Mayor Bill de Blasio became the 24th person to declare their candidacy for the 2020 Democratic presidential nomination Tuesday. That means when the first two-night Democratic debate rolls around on June 26 and 27, four people will be squeezed out. 

The Democratic National Committee set up a system for the first two debates of this cycle in anticipation of such a huge field. The DNC wanted to avoid what happened to Republicans in the 2016 race. When the GOP couldn't fit all 17 candidates on one stage, debates featured a secondary debate -- what some jokingly called the kids' table -- with the lowest-polling candidates.

Every candidate who took part in at least one secondary debate was out of the race by mid-February of 2016. Then-candidate Donald Trump was never in a kids' table debate. 

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The DNC's solution in the 2020 race -- at least for the first two debates -- is to spread it out over two nights. Ten candidates maximum per night. No more than 20 total.

Who will appear on which night? The DNC says that will be chosen at random -- not based on polling. Joe Biden and Elizabeth Warren could appear on the same night or separate nights. Kamala Harris and Bernie Sanders could be side-by-side or 24 hours apart. In other words, no kids' table.

With a maximum of 20, that means at least four of the current 24 candidates will not be seen by a national audience putting their positions against the others in late June and July. One of them -- former U.S. Senator Mike Gravel -- says he doesn't even want to win the nomination, He just wants to get on the debate stage to push the discussion to the left.

There is also no guarantee a total of 20 candidates will make it. The DNC says candidates must hit one of two requirements to qualify. From the DNC website:

Polling Method: Register 1% or more support in three polls (which may be national polls, or polls in Iowa, New Hampshire, South Carolina, and/or Nevada) publicly released between January 1, 2019, and 14 days prior to the date of the Organization Debate. (DNC has selected a specific, lengthy list of qualifying polls).

Grassroots Fundraising Method. Candidates may qualify for the debate by demonstrating that the campaign has received donations from at least (1) 65,000 unique donors; and (2) a minimum of 200 unique donors per state in at least 20 U.S. states. 

According to Huffington Post, four candidates -- not including de Blasio, who just declared -- had not qualified for the debates as of Tuesday. They are Sen. Michael Bennet, D-Colo.; former Sen. Mike Gravel; Miramar, Florida Mayor Wayne Messam; and Rep. Seth Moulton of Massachusetts.

HuffPo says 11 other candidates have qualified with both polling and donations. Six more have qualified with just polling. Spiritual adviser, author and activist Marianne Williamson is the only one to qualify solely through donations.

FiveThirtyEight.com says Montana Governor Steve Bullock, who declared on Tuesday, has also reached the threshold for the debate stage.

If all candidates meet at least one criteria, then the DNC will give priority to candidates who meet both thresholds, followed by those with the highest polling average, then followed by those with the most unique donors.

The field could grow by at least one more. New York City Mayor Bill de Blasio said he will make a decision this week. Former Georgia gubernatorial candidate Stacey Abrams has said she hasn't ruled out a run.