EXCLUSIVE - WATERLOO, IOWA - Former President Donald Trump returns to Iowa on Tuesday with just under four weeks to go until the Hawkeye State's Jan. 15 caucuses lead off the Republican presidential calendar.

And with the first votes in the 2024 White House race fast approaching, Trump remains the commanding front-runner for the GOP nomination as he makes his third straight bid for president.

As Trump returns to Iowa, his top two rivals for the nomination are taking aim at the former president. But Florida Gov. Ron DeSantis and former South Carolina Gov. Nikki Haley, who later served as ambassador to the United Nations in the Trump administration, are also spending plenty of time on the campaign trail in Iowa blasting each other. 

"If you punch me, I punch back," Haley's repeatedly emphasized this week on the campaign trail, as she pushes back against attack ads from a DeSantis-aligned super PAC that are running on Iowa television.

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Haley charges that "Ron DeSantis has lied in every one of his commercials" and stresses that "if you've got to go out, tell lies about someone to win, you don't deserve to win."

Asked about the ads, DeSantis in exclusive interviews with Fox News in Ankeny and Bettendorf, Iowa, on Monday fired back.

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"Her problem is that she doesn't have a conservative record. She's an establishment candidate," he said.

Since he launched his White House campaign in the spring, DeSantis for months was the clear No. 2 rival to Trump in the Republican nomination race.

Ron DeSantis in Iowa

Florida Gov. Ron DeSantis, a 2024 Republican presidential candidate, takes a photo with Iowa voters following a campaign event on Dec. 18, 2023 in Bettendorf, Iowa (Fox News - Paul Steinhauser)

Haley has enjoyed plenty of momentum in the polls in recent months, thanks in part to well-received performances in the first three GOP presidential primary debates. She leapfrogged over DeSantis for second place in New Hampshire, which holds the first primary and votes second after Iowa. And she's in second place in her home state, another crucial early voting state that holds the first southern contest.

Haley's also working to make a fight of it in Iowa, as she's pulled closer to DeSantis, who remains a very distant second to Trump in the latest polls.

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Last week, Haley won the backing of popular Republican Gov. Chris Sununu of New Hampshire. And she was endorsed a couple of weeks ago by Americans for Prosperity (AFP) Action, the political wing of the influential and deep-pocketed fiscally conservative network founded by the billionaire Koch Brothers. AFP Action has pledged to spend tens of millions of dollars and mobilize its formidable grassroots operation to boost Haley and help push the Republican Party past Trump.

Nikki Haley turns up the volume on Ron DeSantis as they both campaign in IOwa

Republican presidential candidate Nikki Haley speaks during a town hall, Monday, Dec. 18, 2023, in Nevada, Iowa. (AP Photo/Charlie Neibergall)

But Haley's momentum this autumn has led to a much larger target on her back.

DeSantis charged in his Fox News interview that Haley was being funded by "liberal donors in California, Wall Street, liberal Wall Street executives."

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"They're not funding her because she's going to be a change agent. They're funding her because they know she represents managed decline. She will not do what needs to be done to reverse the decline of this country. She also cannot beat Donald Trump in a one-on-one. She doesn't have support from conservatives," he argued.

Haley says the attacks she's facing are a sign of her momentum in the Republican race and pledges, "I'm going to keep telling you the truth because that's what we need to do."

Nikki Haley and Ron DeSantis

Florida Governor Ron DeSantis (R) and former UN ambassador Nikki Haley gesture as they speak during the fourth Republican presidential primary debate at the University of Alabama in Tuscaloosa, Alabama, on December 6, 2023. (JIM WATSON/AFP via Getty Images)

"I think they just see it as the rest of political observers do in that the fight is for second place," longtime Iowa-based Republican strategist Jimmy Centers told Fox News. 

Centers, a veteran of multiple presidential campaigns, gubernatorial and congressional campaigns, and who served as communications director for then-Gov. Terry Brandstad and for current Gov. Kim Reynolds, emphasized that "to march on to New Hampshire and make a strong case, Gov. DeSantis needs to finish in second place."

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"Ambassador Haley, seeing how she's polling in New Hampshire, understands that if she can secure that second place finish, it's going to be really hard for Gov. DeSantis to march on to New Hampshire and beyond," Centers argued.

DeSantis reiterated to Fox News that "we're going to win here in Iowa."

And he predicted that the caucuses "will be very clarifying in terms of who is a real deal and who's not. So we look forward to that."

Asked if he'll move on to New Hampshire regardless of his finish in Iowa, DeSantis quickly said, "Of course. Yeah, absolutely. Of course."

But Centers, pointing to the increased verbal attacks between DeSantis and Haley, said that if they "keep poking at each other, it only benefits Trump."

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.