Poll: Sanders takes lead in Iowa less than a month before vote

Sen. Bernie SandersBernie SandersSanders joins Biden atop 2020 Democratic field: poll The Hill's Morning Report - Trump trial begins with clashes, concessions Trump on Clinton's Sanders comments: 'She's the one that people don't like' 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 WarrenElizabeth Ann WarrenSanders joins Biden atop 2020 Democratic field: poll The Hill's Morning Report - Trump trial begins with clashes, concessions Hillary Clinton tears open wound with her attack on Sanders MORE (D-Mass.), who registered 17 percent in the survey.

Former South Bend, Ind., Mayor Pete ButtigiegPeter (Pete) Paul ButtigiegSanders joins Biden atop 2020 Democratic field: poll The Hill's Morning Report - Trump trial begins with clashes, concessions Hillary Clinton tears open wound with her attack on Sanders MORE and former Vice President Joe BidenJoe BidenSanders joins Biden atop 2020 Democratic field: poll The Hill's Morning Report - Trump trial begins with clashes, concessions Trump says impeachment lawyers were 'really good' 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 KlobucharAmy Jean KlobucharSanders joins Biden atop 2020 Democratic field: poll The Hill's Morning Report - Trump trial begins with clashes, concessions Sanders holds four-point lead on Biden in new California poll 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 YangAndrew YangSanders joins Biden atop 2020 Democratic field: poll Sanders holds four-point lead on Biden in new California poll Yang highlights outsider status in Iowa ad ahead of caucuses MORE finished just below her, with 5 percent support.

Sen. Cory BookerCory Anthony BookerPatrick backs reparations in unveiling 'Equity Agenda for Black Americans' Booker ahead of Trump impeachment trial: 'History has its eyes on us' Sunday shows preview: Lawmakers gear up for Senate impeachment trial 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 TrumpDonald John TrumpRouhani says Iran will never seek nuclear weapons Trump downplays seriousness of injuries in Iran attack after US soldiers treated for concussions Trump says Bloomberg is 'wasting his money' on 2020 campaign 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.