Still, it’s not hard to imagine cases where the primary is at a stalemate between three or more candidates. And that’s key: almost all no-majority scenarios require three or more Democrats to continue accumulating delegates on a sustained basis.
There are three main factors that work to prevent such a scenario from happening, however:
First, Democratic rules only award delegates to candidates who get at least 15 percent of the vote in particular states or districts. It’s not a perfectly bright line — if you’re at, say, 14 percent, you’ll still likely get delegates in some districts but not others. But it’s a fairly bright one. Maybe Andrew Yang or Tulsi Gabbard can command 5 to 6 percent of the vote with their own relatively distinct constituencies — but it won’t net them any delegates.
Second, the early states serve to winnow the field. Only Biden and to a lesser extent Sanders are comfortably above 15 percent in national polls, and even they’re not so far above as to necessarily be in a position to stay there following poor showings in the early states. Meanwhile, Warren and Buttigieg (who isn’t above 15 percent nationally) would almost certainly be in trouble in the absence of early state wins.
And third, our model assumes that candidates are reasonably likely to drop out if they don’t have a shot at the nomination, even if they could complicate life for other candidates. This is the most debatable assumption, so we’ll revisit it in a bit.