The prospect of a contested convention sends chills down the spines of Democratic Party strategists. Read: Donna Brazile.

If no candidate has a majority at the Democratic National Convention in Milwaukee this summer, the party faces the prospect of all their backroom dealings playing out on live television.

“A brokered convention would be an ugly act of self-sabotage,” wrote Edward Burmila on the left-wing Nation website.

Perhaps spurred by these warnings, the remaining non-Bernie candidates dropped out over the past week, endorsing Joe Biden on their way out. But don’t discount a contested convention yet.

How a candidate collects delegates varies from state to state.

Many Republican states are winner-take-all, meaning whichever candidate wins the primary gets that state’s entire slate of delegates.

Donald Trump won 46 percent of the vote in Florida’s primary in 2016, compared to 27 percent from Marco Rubio and 17 percent from Ted Cruz. Since Florida was a winner-take-all state, Trump received all 99 delegates. Winner-take-all states mean a close race can quickly turn into a rout, as one candidate can significantly increase their numbers.

Every state in the Democratic primary, however, awards its delegates proportionally.

In the recent New Hampshire primary, Bernie Sanders and Pete Buttigieg received 26 percent and 24 percent of the vote, respectively. Each walked away with nine delegates. Amy Klobuchar ended up with 20 percent and six delegates. Joe Biden and Elizabeth Warren were both under 15 percent and came away with zero delegates. With every state awarding delegates in this manner, it is more difficult for a single candidate to pull away from the pack – the difference between winning and losing is only a few delegates.

The Democrats have struggled with their nominating process for more than fifty years; ever since Hubert Humphrey became the 1968 Democratic presidential nominee despite winning exactly zero state primaries.

In 1982 they created “superdelegates” who were basically just party bigwigs free to support whomever they wished. This gave party establishment more control over the nominating process.

In 2016 Bernie Sanders trailed Hillary Clinton by only a few hundred delegates, but the superdelegates supported Clinton by more than a 13:1 ratio.

Frustrated, Sanders and his supporters managed to change the rules for the 2020 primary. This year, Democratic superdelegates will not be able to vote on the first primary ballot. However, if no candidate arrives in Milwaukee with a majority, the superdelegates will once again be a deciding factor.

As the votes from Super Tuesday are still being counted, Joe Biden leads with 630 while Bernie Sanders is close behind with 552.

If neither candidate has a majority on the first ballot, things will get interesting.

All bets are off on a second ballot. Not only do superdelegates now take part in the vote, but pledged delegates are now free to vote for whomever they wish. The delegates pledged to Bloomberg, Buttigieg, and Klobuchar, for example, would be free to vote for Joe Biden. Superdelegates would likely support Biden as well, according to the New York Times.

If this happens, it would only further outrage Sanders supporters who already believe that the 2016 primary was rigged against him.

This is the nightmare scenario Democrats hope to avoid.

Joe Biden’s surprisingly strong showing on Super Tuesday might have made a contested convention less likely, but the math still makes it a distinct possibility.