So say we apply that 15 percent threshold to the current national polls. Within the crowded field, only former Vice President Joe Biden and Sens. Bernie Sanders and Elizabeth Warren are polling above that threshold. (Hypothetically, someone like South Bend, Indiana, Mayor Pete Buttigieg could break into that group, especially given his standing in Iowa polls.) A group of four candidates consistently clustered around or above the 15 percent threshold could complicate the race for delegates. But is there any real history of that sort of logjam in Democratic presidential nomination politics?

The short answer is: No. The current 15 percent threshold has been in effect since the 1992 Democratic primary,2 and since then there has never been a primary or caucus in which four candidates have earned more than 15 percent of the vote state- or territory-wide. But there have been several instances in which three candidates have surpassed that threshold in a single contest, as you can see in the table below.