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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 poll 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, with 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."

The new poll shows that 24 percent of Republican caucus-goers approved of Trump skipping the debate, 29 percent disapproved, and 46 percent said that Trump's decision made no difference.

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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 attendees 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.

And as the candidates careen toward 7pm CST Monday night, when doors will be shut for hopeful caucus-goers, their rhetorical punches have been coming at a faster pace.

On Thursday night in Burlington, Iowa, Sanders, who has vowed to keep his campaign focused on the “issues,” listed a number of policy positions where he differs from Clinton.

“It is great to be for gay rights, after you insult the entire gay communtiy by supporting DOMA,” said Sanders then referring to President Bill Clinton’s signing of the Defense of Marriage Act with candidate Clinton’s support.

On Saturday, in response to one of the campaign's senior strategists asserting that Sanders has run the “most negative” Democratic primary campaign ever, Clinton told NBC’s Monica Alba that she didn’t disagree with that statement.

Clinton has furthermore been asserting that many of Sanders’ ideas are impractical, highlighting his desire to push for universal single-payer health care if elected president.

These battles of words have also led to a number of turnout battles as both candidates have held events in the same cities on the same nights.

On Friday evening, the former president and Secretary Clinton held an event in the Col Ballroom in Davenport in front of 1,500, which the Des Moines Register characterized as one of the “biggest, most boisterous crowds” the candidate has seen this cycle. Across town, Sanders and activist Cornel West commanded a raucous Danceland Ballroom of 1,000.

Only a few hours later, Sanders packed a room at the Grand River Center in Dubuque with 1,300 attendees all waving campaign-provided American flags, when earlier in the day, Clinton spoke to 460 people at the north eastern city’s Five Flags Center.

Clinton earned the Des Moines Register Editorial Board’s endorsement last week.

“In the final analysis, Iowa Democrats will have to choose between the lofty idealism of Bernie Sanders and the down-to-earth pragmatism of Hillary Clinton,” read the endorsement.

Since then, a number of newspaper endorsements have followed suit, including the New York Times’ editorial board Saturday morning.

Sanders has now incorporated a positive and encouraging line for his supporters firmly into his stump speech: “If voter turnout is high, we will likely win.”

But he often adds a caveat that if voter turnout is low, he will lose the Iowa caucuses.