When Ted Cruz and John Kasich finally suspended their campaigns for the Republican nomination in May of 2016, Donald Trump had collected 40.2% of primary votes. This total fell well short of a majority and represented the fourth-lowest total of any nominee in the modern era at the time they clinched the nomination. Yet, Trump managed to play his plurality of the votes into nearly 70% of delegates at the Republican convention in Cleveland that summer.

This outsized support was the result of the GOP’s “winner-take-all” structure for some of its primaries. For example, Trump received all of Michigan, Illinois, and Florida’s delegates without winning a majority of the vote in any of those states. Had the GOP’s primary rules prescribed proportional allocation of delegations similar to the Democrats’ rules, Trump may have failed to nail down the nomination prior to the convention -- and would likely have faced an uphill battle to claim the GOP mantle at the convention.

Democrats may find themselves in a similar situation this year. Faced with the largest primary field in modern American history, Democrats still have eight candidates battling for their party’s line on the November ballot (despite 20 candidates -- 20! -- having already left the race). However, unlike its adversary, the Democratic Party relies on proportional allocation of delegates. Nate Silver provided a useful summary of how this process works at FiveThirtyEight, but it is worth reviewing briefly here:

Two types of delegates are allocated in the Democratic Party contests: statewide delegates (who are awarded based on the overall result in a particular state); and local delegates (who are awarded on the basis of congressional district, county, or state legislative district results, depending on the state).

Delegates are awarded proportionately to individuals who obtain at least 15% of the vote either statewide or at the local level. If you receive at least 15% statewide, you get a proportionate share of statewide delegates; if you receive a least 15% in one of the local jurisdictions, you receive a proportionate share of the delegates from that jurisdiction.

About 35% of delegates are awarded at the state level, and about 65% are awarded at the local level.

In addition, the 2020 party rules preclude superdelegates from voting on the first ballot at the convention. The implication is that to win the nomination outright, a Democrat will need to capture a majority of delegates during the actual primary contests. Yet the practice of proportional allocation casts doubt on the ability of any 2020 candidate to meet this exacting threshold. The 40.2% of contested votes Trump won in 2016 might prove insufficient for one of this year’s Democrats to capture the nomination, and as it stands, neither Bernie Sanders nor Pete Buttigieg nor Amy Klobuchar is anywhere close to that number.

Winning a majority of delegates obviously becomes easier if the field dwindles significantly after South Carolina and Nevada. But a problem arises: none of the top seven candidates seem likely to drop out before Super Tuesday. Biden, Sanders, Elizabeth Warren, and Buttigieg all raised at least $20 million in the fourth quarter of 2019, and that’s not to mention Michael Bloomberg and Tom Steyer (who have functionally unlimited assets), and Klobuchar, who will certainly see a sustained fundraising bounce in the wake of her unexpected third-place finish in New Hampshire. As such, none of these contestants can be counted on to run out of money in the near future. Nor can they be expected to run out of motivation. The 2016 example indicates that Sanders will remain in the running until the bitter end -- mathematical elimination is no obstacle to a movement candidate like himself. Likewise, Buttigieg and Klobuchar have performed well enough in the first few states to reach at least Super Tuesday, and neither Biden nor Warren seems likely to quit before then. Bloomberg, meanwhile, will not even begin to compete until the first four states have passed, which means that his presence can be counted on as well. The only potential dropout is Steyer, who spent a fortune on goosing his poll numbers in the early states and may be reliant on a strong finish in at least one of those contests in order to continue.

The primary calendar itself exacerbates the problem of candidates staying in the race. Iowa, New Hampshire, South Carolina, and Nevada allocate 6% of delegates and take the contest through February 25. In the following three weeks, however, an additional 54% of delegates will be up for grabs on three primary dates -- March 3, March 10, and March 17. As such, viable candidates only need enough money for a month more of campaigning in order to see the majority of delegates allocated. For the top-tier candidates -- some of whom have already been campaigning for a year -- that opportunity may be too much to pass up.

If no clear winner has emerged by March 17, it is hard to understand why any of the contenders would abandon the contest; after all, with the delegate count hopelessly fragmented and a contested convention an unknown entity, a candidate would have little to lose by remaining in the competition. Suppose for the sake of argument, however, that the field narrowed to a single moderate and a single progressive (with likely Biden, Buttigieg, or Klobuchar in the former role and Sanders in the latter). In that case, one candidate would still need to run up strong numbers in order to overcome the February and March splits, a daunting proposition in a party closely divided between moderates and progressives.

Then there’s the Bloomberg of it all. The former New York City mayor has staked his campaign on competing in the later primaries and has the personal wealth to advertise his way to 15% in a tight race. His campaign could effectively spoil any prospect of a decisive victory for either wing of the party. It may well be that Bloomberg’s candidacy is premised on forcing a brokered convention. Polling near 15% nationally, it is unlikely that he believes he can capture a majority of primary delegates, particularly after skipping the first four states.

Proportional allocation, the sheer number of candidates, their financial resources, the compactness of the primary schedule, and Bloomberg’s specter all raise the probability of a contested convention to a level underestimated by the national media. None of this is to say that a brokered Democratic National Convention is a foregone conclusion; as punditry goes, it would be unwise to predict an event that has not occurred in several decades. Yet given its potentially monumental consequences on the 2020 general election, it deserves to be considered with greater seriousness.

Brett Parker is a JD/PhD student at Stanford University.