With five days to go until Iowa’s caucuses kick off the presidential nominating calendar, a new poll shows former Vice President Joe Biden and Sen. Bernie Sanders of Vermont fighting for the lead in the state’s Democratic caucuses, with former South Bend, Ind., Mayor Pete Buttigieg and Sen. Elizabeth Warren close behind.

And the Monmouth University survey released Wednesday also indicates that nearly half – 45 percent – of likely Democratic presidential caucuses goers in the Hawkeye State say they are open to switching support on caucus night to another candidate.

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Biden stands at 23 percent support and Sanders at 21 percent in the poll, which was conducted Thursday through Monday. The former vice president’s 2-point edge over the populist independent senator who’s making his second straight White House bid is well within the survey’s sampling error.

Buttigieg – who at 38 is the youngest candidate in the Democratic presidential field – stands at 16 percent, with Warren of Massachusetts at 15 percent.

The poll indicates Sen. Amy Klobuchar of neighboring Minnesota at 10 percent, with billionaire environmental and progressive advocate Tom Steyer at 4 percent and tech entrepreneur Andrew Yang at 3 percent. Sen. Michael Bennet of Colorado and Rep. Tulsi Gabbard of Hawaii – who are campaigning heavily in the first primary state of New Hampshire rather than in Iowa – stand at 1 percent, with former Massachusetts Gov. Deval Patrick and former Rep. John Delaney of Maryland registering at less than 1 percent.

Former New York City Mayor Mike Bloomberg – who’s skipping the early voting states of Iowa, New Hampshire, Nevada, and South Carolina – was not tested in the Monmouth poll.

“Caucus electorates are the most difficult to model in polling. The smartest takeaway from this, or any Iowa poll for that matter, is to be prepared for anything on Monday,” Monmouth University Polling Institute director Patrick Murray said.

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The two most recent live telephone operator surveys in Iowa prior to the new Monmouth poll pointed to slightly different results. Biden enjoyed a 6-point lead over his 2020 Democratic rivals in a USA Today/Suffolk University survey released Sunday. But Sanders was sitting on a 7-point lead over the rest of the field in a New York Times/Siena College poll released on Saturday.

But the new survey points to the possibility of five White House hopefuls reaching viability in Iowa – where a candidate needs to reach 15 percent at a Democratic caucus site to secure delegates to this summer’s Democratic nominating convention. Supporters of candidates who fail to reach 15 percent support at a caucus site can realign during a second round.

The poll asked caucusgoers to name a candidate they have in mind as a second choice. When these are combined with initial preferences, Biden (39 percent), Warren (34 percent), Sanders (32 percent), and Buttigieg (29 percent) are bunched together. They are trailed by Klobuchar (22 percent), Steyer (10 percent), and Yang (7 percent) as either a first or second choice.

The poll suggests that if Klobuchar and Yang remain viable in some caucus precincts, the race should remain tight. But if only the top four candidates – Biden, Sanders, Buttigieg, and Warren – remain viable, Biden appears to benefit slightly more than his top-tier rivals.

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Murray noted that “Klobuchar’s performance could be a real game changer in the final delegate allocation out of Iowa.”

The Monmouth poll was conducted Jan. 23-27, with 544 voters likely to take part in the Feb. 3 Iowa Democratic presidential caucuses questioned. The survey’s sampling error is 4.2 percentage points.