Former UN Ambassador Nikki Haley has edged ahead of Florida Gov. Ron DeSantis in the final poll of likely Iowa caucusgoers before Monday's vote.

Why it matters: Former President Trump is expected to win by a large margin on Monday, but DeSantis is staking much of his campaign on a second place finish in Iowa.

Zoom in: Trump polled as the first choice for 48% of likely caucusgoers in the NBC News/Des Moines Register/Mediacom Iowa poll, down from 51% in December.

• Haley is at 20%, up from 16% in December.
• DeSantis is at 16%, down from 19% in December.
• Entrepreneur Vivek Ramaswamy is at 8%, up from 5% in December.

Zoom out: The last two Iowa GOP caucuses were far tighter heading into election day, as NBC election guru Steve Kornacki reminded people on Saturday.

• In 2016, Trump led Sen. Ted Cruz in the last poll ahead of the caucuses, but ended up taking second to Cruz.
• In 2012, former Sen. Rick Santorum surprised the pollsters by narrowly beating eventual nominee Mitt Romney despite being in third in the final pre-caucus poll.

Between the lines: Trump (49%) and DeSantis (23%) scored far better than Haley (9%) when it came to having "extremely enthusiastic" supporters.

• "The deep data on (Haley) suggest she looks stronger in the poll than she could on caucus night," said J. Ann Selzer, who conducted the poll.

The bottom line: The biggest x-factor in Iowa could be the weather.

• The forecast HIGH in Des Moines on Monday is currently -1°.

Methodology: "The poll of 705 likely Republican caucusgoers was conducted Jan. 7-12 and has a margin of error of plus or minus 3.7 percentage points."

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