Save for a few blips in both directions, former Vice President Joe Biden spent all of 2019 dominating the Democratic presidential primary with about 30% of the vote in national polls. His support hasn’t flamed out, and his competitors’ cash has only grown, increasing the odds that no candidate will complete the primary season with a majority of delegates. The result would be the ever-elusive contested convention that political nerds have dreamed of for decades.

Unlike the 2016 Republican primaries, Democrats have no winner-take-all states. In most states, often subdivided into congressional districts, candidates just have to earn at least 15% of the primary vote to obtain pledged delegates. Whereas President Trump could clean up the overwhelming majority of delegates without a majority of the popular vote in the 2016 Republican primary, candidates earning at least 15% in enough districts could hold out hope that no competitor takes a majority of the total delegates.