Polls testing the waters in the first-in-the-nation Iowa Democratic caucuses show a fluid race with dramatic swings in support among the four top-tier candidates.

A Monmouth University poll released Monday shows former Vice President Joe Biden leading the field with 24% support among likely Democratic caucusgoers, a 5-point increase since his second-place showing of 19% support in a November Monmouth Iowa poll.

Vermont Sen. Bernie Sanders came in second with 18%, up 5 points since November. Former South Bend, Indiana, Mayor Pete Buttigieg was at 17%, down from his first-place finish of 22% in November, and Massachusetts Sen. Elizabeth Warren dipped 3 points to 15%. Minnesota Sen. Amy Klobuchar was in a distant fifth place, with 8% support, and no other candidate received more than 4%.

The poll results came from 405 registered voters in Iowa who said they were likely to attend the Feb. 3 Democratic presidential caucuses reached by phone from Jan. 9-12. The poll has a margin of error of plus or minus 4.9%.

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The Monmouth poll tells a dramatically different story than a Des Moines Register/CNN/Mediacom Iowa poll released Friday that had Biden in fourth place with 15% support, Sanders leading the pack at 20%, and Warren and Buttigieg in second and third with 17% and 16%, respectively.

As the top four candidates increasingly take swipes at each other in the tight race, voter preferences are poised to change again.

“Even among the top contenders, about 4 in 10 supporters are still open to changing their initial preference by caucus night. There are only three weeks to go, but this race is far from over,” said Patrick Murray, director of the Monmouth University Polling Institute.

In the RealClearPolitics average of Iowa primary polls, Biden leads with 20.7%, Sanders has 20.3%, Buttigieg has 18.7%, and Warren has 16%.