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Trump regains lead over Cruz in Iowa, Clinton barely leads Sanders: Poll

Hillary Clinton arrives at her rally in Des Moines, Ia., Jan. 29, 2016. (Photo by Mark Peterson/Redux for MSNBC)
Hillary Clinton arrives at her rally in Des Moines, Ia., Jan. 29, 2016. 

Donald Trump has surged past Ted Cruz in Iowa, while Hillary Clinton is holding a three-point lead over Bernie Sanders, according to the final Des Moines Register/Bloomberg Politics before the Iowa caucuses.

Trump captures the support of 28 percent of likely caucus-goers, compared to 23 percent for Cruz, 15 percent for Florida Sen. Marco Rubio and 10 percent for former neurosurgeon Ben Carson.

On the Democratic, the data shows Clinton up over Sanders 45 to 42 percent, with just three percent for former Maryland Gov. Martin O'Malley.

The survey from highly-respected pollster Ann Selzer comes just about 48 hours before voters will meet at the state's 1,681 precincts for Monday night's caucuses.

The Iowa poll is widely viewed as a "gold standard" in the industry because of its record of accurately predicting past contests. Selzer forsaw Barack Obama's victory over Hillary Clinton in the 2008 caucuses, and she pegged Rick Santorum's late surge over Mitt Romney in 2012.

The poll was conducted January 26-29, and the margin of error is four percentage points.

The GOP

The poll shows a continuing slide for Cruz, who bested Trump by 10 points in the same poll in December. In early January, he led the real estate mogul by three points.

Trump's supporters are also the most set in their choice, 71 percent saying their mind is made up to support him on Monday. That's compared to 61 percent for Cruz and 47 percent for Rubio.

As Cruz rose in the polls through December, Trump began launching attacks against the Texas senator, targeting his birth in Canada, questions over his support for a path to legal status for undocumented immigrants and criticism for taking out loans from Goldman Sachs and Citibank for his 2012 senate campaign.

Last week, after Trump bailed on the GOP's final Iowa debate, Cruz challenged Trump to a debate that would be "90-minutes, Lincoln-Douglas, mano-a-mano, Donald and me."

Cruz has taken hits over the past two weeks, starting with Iowa Gov. Terry Branstad suggesting Cruz would be "damaging" to the state because of his position on the Renewable Fuel Standard, which requires ethanol be used in the U.S. fuel supply.

Cruz has also taken consistent heat from the pro-ethanol group America's Renewable Future, leading farmers to confront Cruz for his position on the issue at nearly each one of his campaign stops over the past month.

In a poll conducted by Ann Selzer's polling firm in October, 61 percent of Republicans in the state said they would be more likely to back a candidate who favors growth in renewable fuels.

And Ben Carson - who in mid-October led Trump by nine points in the poll - is still pulling significant support. Carson's campaign has said the candidate needs to finish in the top four to continue beyond Iowa

Trump's ground game - a constant point of skepticism by outsiders - will be tested on Monday.

The Iowa Republican Party is preparing for record turnout - but the extent of the surge of caucus-goers is in question.

Rubio's campaign, widely criticized for its lack of organization in the state through the summer and fall, increased its presence, along with Rubio himself, in the state over the final two months of the race.

The Democrats

The topline Iowa results for the Democratic race are largely consistent with the previous poll's findings, which showed Clinton leading Sanders by two points.
Unlike in 2008, when a majority of participants in the caucuses attended for the first time, just a third of likely caucus-goers in this survey are first-time caucus-goers. Those voters lean heavily towards Sanders.And more than eight-in-ten Clinton supporters say they have made up their minds to support her on Monday night.Both Sanders and Clinton have been crisscrossing primarily the eastern part of the state nonstop in the final days in hopes of drumming up enthusiasm and support.

Sanders' keys to victory

Jan. 30, 201605:50

This article originally appeared on NBCNews.com.