With 24 days until the first-in-the-nation Iowa caucuses, Bernie Sanders leads the Democratic presidential field in the state's most respected poll while Joe Biden lags in fourth place.

The Vermont senator has 20% support in the Des Moines Register/CNN/Mediacom poll of likely Democratic caucusgoers, a five-point jump in support since the last time the institution polled Iowa voters in November. Fellow candidate Massachusetts Sen. Elizabeth Warren is in second place with 17%.

Pete Buttigieg, the former South Bend, Indiana, mayor, came in third with 16%, a 9-point drop from his 22% first-place finish in November. Biden held 15% support in the poll, the same percentage as in November.

The poll results came from 701 registered Iowa voters reached by phone from Jan. 2 to 8 who said they would definitely or probably attend the Democratic caucuses on Feb. 3. It has a maring of error of plus or minus 3.7%.

A first-place finish in Iowa accompanied by a Biden drop is key to Sanders's path to the Democratic presidential nomination, but preferences of Iowa voters can change quickly.

“There’s no denying that this is a good poll for Bernie Sanders. He leads, but it’s not an uncontested lead,” said pollster J. Ann Selzer, president of the company that conducted the poll. “He’s got a firmer grip on his supporters than the rest of his compatriots.”

Only a minority of the likely caucusgoers, 40%, said that they are settled on their preferred candidate, while 45% said they could be persuaded to support someone else, and 13% have not yet picked a favorite candidate.

Before Friday's poll, Sanders led Iowa in the RealClearPolitics average of primary polls at 22%, followed by Buttigieg at 21.7%, Biden at 20.3%, and Warren at 15.3%.