Bernie Sanders led with 28% support from Democrats in a statewide Iowa poll released on the eve of Monday’s caucuses.

In the Emerson College poll of likely Democratic caucus-goers, Joe Biden came in second with 21%, followed by Pete Buttigieg with 15% and Elizabeth Warren with 14%. Amy Klobuchar was fifth, with 11%.

Several factors complicate the poll results. Caucus-goers whose favored candidate doesn’t attain at least 15% support in their precinct will get to pick a fallback choice in a second round, which has the potential to remix the rankings. And this year, four competitive candidates are packed fairly closely at the top of a historically large field.

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