FIRST ON FOX - With a month to go until the first votes in the Republican presidential nomination race, former New Jersey Gov. Chris Christie is turning up the heat on 2024 GOP rivals Florida Gov. Ron DeSantis and former South Carolina Gov. Nikki Haley.

Tell It Like It Is, a super PAC supporting the former New Jersey governor's presidential campaign, is launching a new multimillion-dollar ad blitz that takes aim at DeSantis and Haley for not forcefully making the case against former President Trump.

Trump remains the commanding front-runner for the Republican nomination as he makes his third straight run for the White House.

The spot, shared first with Fox News on Friday, includes a clip of Christie from last week's fourth GOP presidential primary debate, where he repeatedly chastised his rivals for failing to verbally confront Trump. Christie is a one-time Trump ally turned vocal Republican critical of the former president.

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"Folks like these three guys on the stage make it sound like his conduct is acceptable. Let me make it clear. His conduct is unacceptable. He’s unfit," Christie says in the clip used in the commercial.

The ad ends with the narrator emphasizing that Christie is "the only Republican with the courage to tell the truth. And the experience to get it done."

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Trump made history earlier this year as the first former or current president to be indicted for a crime, but his four indictments — including in federal court in Washington, D.C., and in Fulton County court in Georgia on charges he tried to overturn his 2020 presidential election loss — have only fueled his support among Republican voters.

Christie, who has been amplifying his attacks on Haley and DeSantis for weeks for taking it easy on Trump, charged during the debate at the University of Alabama that it was "ridiculous" that his rivals would not discuss Trump. "I'm in this race because the truth needs to be spoken," he stressed. "He is unfit to be president."

Trump skipped the fourth GOP presidential nomination debate

Republican presidential candidate Florida Gov. Ron DeSantis, third from left, speaks as former New Jersey Gov. Chris Christie, left, former U.N. Ambassador Nikki Haley and businessman Vivek Ramaswamy, right, watch during a Republican presidential primary debate on Wednesday, Dec. 6, 2023. (AP Photo/Gerald Herbert)

The super PAC tells Fox News that they will spend $3 million to run the ad on TV starting Friday in New Hampshire, the state that holds the first primary and second overall contest in the GOP nominating calendar. They showcase that they will spend an additional half a million dollars to run the spot digitally.

"‘Unacceptable’ is designed as the first of a series of ads appealing to New Hampshire’s unique position to reset the course of the nomination process," Tell It Like It Is Chairman Bill Palatucci said. "This ad starts the 30 Day march to January 23 when Granite State voters have the opportunity to send a message to their fellow Republicans that Chris Christie is the truth teller America deserves."

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Just as he did in his unsuccessful 2016 White House campaign, Christie is once again devoting nearly all of his time and resources to New Hampshire, where independent voters and moderates have long played a crucial role in the state's famed primary.

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Former New Jersey Gov. Chris Christie, a 2024 Republican presidential candidate, headlines a town hall in Londonderry, New Hampshire, on Dec. 13, 2023. (Fox News - Paul Steinhauser)

The latest public opinion polls in New Hampshire indicate Trump holds a very large and formidable double-digit lead, but he has under 50% support, with Haley in the upper teens and Christie a few points back.

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Trump also holds a commanding lead in the most recent surveys in Iowa, whose Jan. 15 caucuses kick off the Republican nominating calendar, with DeSantis a distant second, followed by Haley. Christie, who has no plans to campaign in Iowa, and multimilionaire entrepreneur and first-time candidate Vivek Ramaswamy, who is barnstorming through the Hawkeye State, are in the single digits in the polls.

The Tell It Like It Is ad is being released on the same day that Christie's campaign launched their first commercial of the 2024 election cycle.

The campaign's ad criticizes DeSantis and Haley for attacking each other rather than Trump.

"There's only one candidate trying to stop Trump," the narrator says in the spot, which the Christie campaign says it's spending six figures to run in New Hampshire.

The campaign and the super PAC are barred by law from coordinating.

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