A new Des Moines Register/CNN/Mediacom poll has Vermont Senator Bernie Sanders leading the race in Iowa 24 days out from Caucus Day with 20% support among likely Democratic caucus-goers.

Sanders is followed by Massachusetts Senator Elizabeth Warren with 17%, former South Bend Mayor Pete Buttigieg at 16% and former Vice President Joe Biden at 15%.

Sanders' support is up 5 points compared to the Register's poll in November. Warren's support ticked up one point, while Buttigieg's plummeted 9 points and Biden's support did not change.

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"There's no denying that this is a good poll for Bernie Sanders. He leads, but it's not an uncontested lead," said J. Ann Selzer, president of Selzer & Co., which conducted the poll told the Des Moines Register. "He's got a firmer grip on his supporters than the rest of his compatriots."

The poll, which was released four days before the Democratic debate in Des Moines, does not put any new candidates on the stage. The deadline to qualify for the debate is midnight Friday. Biden, Buttigeg, Klobuchar, businessman Tom Steyer, Sanders and Warren have already qualified.

Outside of the top tier of candidates, Minnesota Senator Amy Klobuchar saw her support remain at 6%. She was followed by entrepreneur Andrew Yang at 5% and New Jersey Senator Cory Booker at 3%. All other candidates were at or below 2%.

The poll shows that many likely caucus-goers still haven't fully settled on a candidate. Only 40% of likely caucus-goers say they have made up their mind on who they plan to support, which is up 10 points from November. However, 45% of respondents said they could still be persuaded to pick a different candidate to support and 13% said they have yet to pick a favorite.

The most recent CBS News Battleground Tracker Poll similarly found a close race between the top tier of Democratic candidates, with Sanders, Biden and Buttigieg tied for first place with 23% support.

The Iowa caucuses, which will be the first nominating contest of the 2020 Democratic primary, will be held on February 3rd. Seven of the last nine Democratic nominees have won the Iowa caucuses, including Hillary Clinton in 2016 and Barack Obama in 2008.

The survey, which began the day the United States killed top Iranian military general Qassem Soleimani, found that 57% of likely Democratic caucus-goers said foreign policy is an "extremely important issue for them." Meanwhile, respondents also said healthcare (68%), climate change (68%) and the gap between the rich and poor (59%) were extremely important issues.

The poll, which was conducted from January 2 to January 8, surveyed 701 likely Democratic caucus-goers and has a margin of error of plus or minus 3.7%.