The poll offered positive standings for former Vice President Joe Biden, South Bend Mayor Pete Buttigieg and Warren, but a potentially concerning result for Sanders.

Biden and Warren are dead even, each pulling 23 percent of the votes. South Bend Mayor Pete Buttigieg is polling at 16 percent. Sanders is polling at 13 percent. No other candidates have received more than 5 percent support for the caucus, which is the first of the 2020 election and is scheduled for February 3.

“The good news for Biden is he did not lose much ground since March’s poll that had him at 25 percent of the vote,” Spencer Kimball, the director of Emerson Polling, said.

Warren has benefitted from Sanders’ drop from 24 percent support in March to 13 percent support in October, according to the pollster, and has notably pulled over voters who selected Sanders in 2016. The Massachusetts lawmaker is drawing 26 percent of the vote among individuals who chose Sanders, rather than Clinton, in the 2016 Iowa caucus. Sanders is pulling 19 percent of his 2016 Iowa caucus voters, and Buttigieg is drawing 16 percent of this pool.

While the Massachusetts senator is gaining traction among former Sanders voters, Biden seems most appealing to Iowa Democrats who chose Hillary Clinton in the 2016 Caucus. The former vice president has captured 42 percent of this pool, while Warren has drawn 22 percent, and Buttigieg has pulled 13 percent.

Warren has overtaken Sanders in polls and currently appears to be the biggest potential threat to Biden. However, Sanders, following a heart attack and questions about his health, will be formally earning the endorsement of Representative Alexandria-Ocasio Cortez on Saturday. Minnesota Representative Ilhan Omar, another progressive freshman legislator, tweeted on Wednesday that she was “proud to endorse” Sanders.

For months, Biden held the sole position as the Democratic frontrunner. But Warren has been eating into that lead. Voters say her detailed policy plans have helped build her appeal.

At a New York rally last month in Washington Square Park, young Warren fans who spoke to Vice depicted Warren as more pragmatic than Sanders; supporters of the Vermont senator, in turn, have expressed concerns about Warren’s description as a “capitalist” and how progressive she will be if she wins office.

As Warren continues gaining in polls, she has begun facing more frequent attacks from other candidates. Biden questioned the senator’s “credibility” this week, focusing on her plan to implement Medicare-for-All.

“It’s fascinating that the person who has a plan for everything has no plan for the single most consequential issue in this election in the minds of the American people across the board,” he said a day after the debate on Tuesday, where candidates including Buttigieg and Senator Amy Klobuchar directly challenged Warren on her policies.