Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.) has taken the lead in Iowa, according to a Des Moines Register/CNN poll released on Friday that shows the Vermont senator jumping past his top rivals after a third-place finish in the same survey in November.

The poll, widely considered the most authoritative in Iowa, shows Sanders with the support of 20 percent of likely Democratic caucusgoers. He's trailed closely by another progressive, Sen. Elizabeth Warren Elizabeth WarrenWarren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon No new taxes for the ultra rich — fix bad tax policy instead MORE (D-Mass.), who registered 17 percent in the survey.

Former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq A socially and environmentally just way to fight climate change MORE and former Vice President Joe Biden Joe BidenCast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response Biden tells CNN town hall that he has benefited from white privilege MORE round out the top four, notching 16 percent and 15 percent support, respectively.

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Still, Sanders’s lead in Iowa is narrow – within the poll’s 3.7 percent margin of error – suggesting that the race in the Hawkeye State remains wide open with less than a month to go before the first-in-the-nation caucuses.

The Des Moines Register poll shows that Iowa remains a four-person race. No other candidate managed to register in double digits. Sen. Amy Klobuchar Amy KlobucharEPA delivers win for ethanol industry angered by waivers to refiners It's time for newspapers to stop endorsing presidential candidates Biden marks anniversary of the Violence Against Women Act, knocks Trump and McConnell MORE (D-Minn.), an underdog who’s banking on a strong finish in Iowa to lend momentum to her campaign, notched 6 percent in the poll, while former tech executive Andrew Yang Andrew YangDoctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls Buttigieg launches his own podcast MORE finished just below her, with 5 percent support.

Sen. Cory Booker Cory Anthony BookerDHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility Black Voters Matter Fund deploying voter outreach caravans in 12 states to drive turnout MORE (D-N.J.) also failed to gain ground in the poll, coming in with just 3 percent support. That’s unchanged from the Register’s November poll.

The poll is welcome news for Sanders, who rose 5 points since the last Des Moines Register poll was released in November. That survey showed Buttigieg surging to the front of the pack with 25 percent support.

But Buttigieg’s political fortunes in the state appear to be reversing. He’s faced criticism in recent weeks for his fundraising practices, especially from Warren, who pointedly attacked the former Indiana mayor at last month’s Democratic presidential debate for holding a fundraiser at a so-called “wine cave” in California.

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The number of likely caucusgoers who say their minds are made up on who they will support in the Feb. 3 caucuses has risen, as well. Forty percent of respondents said they are sure of their choice. But that still leaves 45 percent who say they could still change their minds, and 13 percent who have not yet picked a favorite candidate, according to the poll.

Things could still change in Iowa in the weeks leading up to the caucuses. The five senators running for the Democratic nomination are facing President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE’s impending impeachment trial, which is expected to begin next week. That means that they will be stuck in Washington, while candidates like Buttigieg and Biden will be free to campaign in the Hawkeye State.

At the same time, the Iowa caucuses are famously difficult to forecast, because unlike primaries, they involve showing up to a specific location at a specific time – and in the dead of winter – while caucusgoers work to persuade fellow voters to support their preferred candidate.

Because caucusgoers can change their minds on caucus night, second-choice preferences are considered crucial. Warren and Buttigieg were the two candidates most frequently mentioned as caucusgoers’ second choices, picked by 16 percent and 15 percent, respectively.

Twelve percent said that Biden is their second choice in the state, while just as many said Sanders is their No. 2 pick, according to the poll.

The Des Moines Register/CNN poll surveyed 701 likely Democratic caucusgoers in Iowa from Jan. 2-8. It has a margin of error of plus or minus 3.7 percentage points.

-- Updated at 6:38 p.m.