The Democratic presidential primary debate stage is filling up fast: By our count, 18 candidates — including newly qualified Rep. Eric Swalwell and self-help author Marianne Williamson — are now eligible for the first two debates, at the end of June and July. But with participation in the first two debates capped at 20 candidates, the Democratic National Committee could soon need a tiebreaker to decide who gets a spot on the stage.

On Thursday, the DNC updated its debate qualification rules to outline how it will handle tiebreakers. If more than 20 candidates qualify under the first set of debate rules, then meeting both the polling and donor requirements will become very important — candidates who do so will get first dibs on debate lecterns. After that, though, things start to get complicated.

If more than 20 candidates hit both the polling and donor thresholds, the 20 candidates with the highest polling average would be included in the debate. Although 18 candidates appear to have qualified for the debate so far, only 11 have done so by meeting both criteria, so there’s still some wiggle room there.

Which candidates are in line to make the primary debates? Democratic presidential candidates by whether and how they have qualified for the first two primary debates, as of May 9, 2019 Qualifies for debates via … Candidate polls donors both Joe Biden ✓ ✓ ✓ Cory Booker ✓ ✓ ✓ Pete Buttigieg ✓ ✓ ✓ Julian Castro ✓ ✓ ✓ Tulsi Gabbard ✓ ✓ ✓ Kamala Harris ✓ ✓ ✓ Amy Klobuchar ✓ ✓ ✓ Beto O’Rourke ✓ ✓ ✓ Bernie Sanders ✓ ✓ ✓ Elizabeth Warren ✓ ✓ ✓ Andrew Yang ✓ ✓ ✓ John Delaney ✓ Kirsten Gillibrand ✓ John Hickenlooper ✓ Jay Inslee ✓ Tim Ryan ✓ Eric Swalwell ✓ Marianne Williamson ✓ Michael Bennet Seth Moulton For candidates deemed “major” by FiveThirtyEight. To qualify via polling, a candidate must reach 1 percent in at least three national or early-state polls from qualifying polling organizations. To qualify via donors, a candidate must have at least 65,000 unique donors with at least 200 donors in at least 20 states. Information released by campaigns is used to determine whether a candidate has hit the donor threshold. If a campaign reached 65,000 donors but did not say whether it had at least 200 donors in 20 states, we assumed that it had met the latter requirement as well. Candidates will have to prove to the DNC that they have met the donor requirements. Sources: Polls, Media reports

If fewer than 20 candidates meet both standards but more than 20 qualify via the polling method, those who meet both criteria would qualify first and the remaining spots would be filled by those with the highest polling average. To calculate this, the DNC is planning to average the top three survey results for each candidate, rounded to the nearest tenth of a percentage point. That is, the tiebreaker will be calculated using the polls where a candidate performed best, not necessarily the most recent polls. If that average results in a tie for the last spot(s) on the stage, the tied candidates will be ranked by the total number of qualifying polls they submitted to the DNC.

However, if fewer than 20 candidates hit both qualifying criteria and fewer than 20 qualify via the polling method, the DNC and its media partners (NBC and Telemundo in June and CNN in July) would first invite all candidates who reach both the polling and donor thresholds and then any others who meet the polling requirement. After that, the remaining debate slots would be filled by those who have the highest number of unique donors.

As things stand, our research shows that 17 candidates have qualified via the polling threshold, which requires candidates to earn at least 1 percent of the vote in three national or early-primary-state polls conducted by qualifying pollsters since the start of 2019. So if three more people hit this mark, no candidate will qualify based solely on having met the fundraising threshold. This could be a challenge for Williamson, who has built her campaign largely on grassroots support — she’s the only candidate so far who has qualified on fundraising alone. On Thursday, she announced that she had met the DNC’s fundraising criteria by receiving donations from at least 65,000 unique donors, including at least 200 individual donors in at least 20 states, but she has earned 1 percent of the vote in just one qualifying survey.

But Williamson is not the only contender who may wind up on the bubble. Two other candidates have not hit either threshold: Sen. Michael Bennet has earned 1 percent support in only one survey, and Rep. Seth Moulton has yet to hit that mark in any qualifying poll. Neither campaign has reported hitting the 65,000-donor threshold either. In fact, a total of eight candidates considered “major” by FiveThirtyEight’s standards haven’t met the donor threshold, so it remains to be seen if 20 people can meet both criteria. If not, the final debate participants will be decided by the polling average.

With so many candidates hovering around 1 percent or so in the polls, a few tenths of a percentage point could make or break a candidate’s chances of qualifying. The debates give candidates a vital chance to distinguish themselves in a crowded field, so these narrow margins could decide who still has any shot at winning the 2020 Democratic presidential nomination.