Former Vice President Joe Biden may have a commanding lead in the Democratic presidential primaries according to most polls, but he is locked in a dead heat with Sen. Bernie Sanders of Vermont in a crucial poll out of Iowa.

An Iowa Starting Line/Change Research Poll finds that 24 percent of likely Democratic caucus-goers support Biden and another 24 percent support Sanders. Mayor Pete Buttigieg of South Bend, Indiana, comes in third at 14 percent, followed by Sen. Elizabeth Warren of Massachusetts at 12 percent, Sen. Kamala Harris of California at 10 percent and former Rep. Beto O'Rourke of Texas at 5 percent.

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The Iowa caucuses, which are the first in the nation, play an outsized influence in determining a party's eventual nominee. If Sanders is able to maintain his strong position relative to Biden on the day of the caucus, he could pull off an upset — and ride that momentum all the way to the Democratic National Convention.

"It’s clearly a very different outcome from our most recent South Carolina poll, where Biden leads among all demographic groups except 18-34 year olds; in Iowa, he and Sanders generally split that vote," 2020 Change principal pollster Jane Loria said. "This is also a weaker result for Biden than our modeling based on other polling we’ve done across the country would have shown: that model would have had Biden up on Sanders by about 10 points or so."

In most national polls, Biden has maintained a decisive lead over both Sanders and the rest of the Democratic field, which now included more than 20 candidates. A CNN poll taken at the end of April showed Biden ahead of the rest of the pack by 24 points, while a Fox News national survey last week had Biden up by 18 points. A Morning Consult poll taken last month found that 36 percent of Democratic primary voters viewed Biden as their top pick in the 2020 primaries, reflecting a 6-point bump after his announcement and giving him a 14-point lead over Sanders, who was at 22 percent. One week later, another Morning Consult poll put him at 40 percent, followed by Sanders at 19 percent and Warren at 8 percent.

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This is not to say that the new polls spells bad news for Warren, who regularly trailing Biden and Sanders in polls despite her solid reputation as a legislator with substantive policy ideas.. Warren does have some favorable metrics in the Iowa survey, which suggest her support could grow later.

"Good news for Elizabeth Warren: her favorability exceeds that of any other candidate in the race and her name recognition is near universal. In some states, we see a large spread between the front-runners and the so-called second-tier in the excitement barometer, but in Iowa the candidates are all pretty tightly clustered," Loria said regarding Warren's performance. "When we ask respondents to identify the five candidates they’re most excited about, 54 percent say Warren, followed by Biden (53 percent), then Harris (53 percent), Sanders (49 percent), and Buttigieg (46 percent).

Biden has run for president on two previous occasions, in 1988 and 2008, while Sanders ran for the first time in 2016. Warren is running for the first time this year.