Trump's GOP clout on the line in high-profile Republican primaries in Pennsylvania, North Carolina, Idaho

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Mehmet Oz responds to conservative Kathy Barnette's late surge in PA Sen. primary

Oz -- facing Barnette, David McCormick, Jeff Bartos and Carla Sands on Tuesday -- sounds off on 'The Story.'

BLUE BELL, PA – Former President Donald Trump, put in a last-minute pitch in for Mehmet Oz, the Senate candidate he endorsed in Pennsylvania’s crowded, combative, and extremely expensive GOP Senate race.

"This is Donald Trump urging you to vote for Dr. Oz on Tuesday," the former president said in an automated call on behalf of Oz on the eve of Tuesday's primary in the key battleground state.

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And Trump called into the cardiac surgeon, author and well-known celebrity physician’s final campaign event and accompanying tele-rally ahead of the primary, stressing that Oz is "never, ever going to let you down. He's a strong guy, smart gentleman…he's going to be a great senator."

Republican Senate candidate Mehmet Oz listens as former President Donald Trump calls into Oz's primary eve rally in Blue Bell, Pennsylvania, on May 16, 2022. (Fox News )

Trump isn't on the ballot, but the strength of his grip over the GOP is being tested in Pennsylvania and a handful of other states holding primaries on Tuesday.

Oz, who until the launch of his Senate campaign late last year was host of TV’s popular "Dr. Oz Show," has been one of the two polling front-runners for a couple of months in the GOP showdown to succeed retiring Republican Sen. Pat Toomey, in a race that may decide whether the GOP wins back the Senate majority in November’s midterm elections.

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Oz has been one of the two combatants in a slugfest with co-front-runner Dave McCormick, a former hedge fund executive, West Point graduate, Gulf War combat veteran and Treasury Department official in former President George W. Bush's administration.

Republican Senate candidate Dave McCormick speaks with supporters at a campaign event in Middletown, Pennsylvania, on May 16, 2022. (Fox News )

The Oz and McCormick campaigns and outside super PACs backing the two contenders since the beginning of the year have spent tens of millions of dollars to run TV, digital and radio ads attacking each other over their conservative credentials and over key issues since the beginning of the year. 

And in recent weeks veteran and conservative commentator Kathy Barnette’s soared in the surveys, making the Republican primary a three-way face-off.

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Since her surge in the polls, Barnette has faced constant incoming fire from her rivals and other Republicans concerned over her lack of vetting and past controversial comments and worries that she’s too extreme to win a statewide general election in a purple state like Pennsylvania.

Republican Senate candidate Kathy Barnette at a campaign event in Scranton, Pennsylvania on May 16, 2022. (Fox News )

Oz has repeatedly taken aim at Barnette over the past week, saying on Fox News’ "Special Report" on Thursday that "she’s raised questions in her own candidacy that she’s refused to answer." And pointing to her 2020 congressional loss, Oz emphasized that "this is a candidate who lost by 20 points when she ran for Congress 18 months ago, so she’s not going to do well in the general election."

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McCormick, in an interview Monday morning with Fox News Digital, emphasized, "I believe I can win the general [election]. I think she [Barnette] would have a much tougher time winning the general."

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The field of major candidates also includes two other wealthy contenders - Jeff Bartos, a real estate developer, philanthropist and 2018 Republican nominee for lieutenant governor, and Carla Sands, a real estate executive and major Republican donor who served as ambassador to Denmark during the Trump administration.

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Through the end of last week, $63 million had been spent by the candidates and outside groups such as super PACs in Pennsylvania's Republican primary, according to data from AdImpact, a nationally known ad tracking firm. And most of that spending has come from the Oz and McCormick campaigns, and the super PACs backing them.

Without the resources available to Oz and McCormick, Barnette by comparison has spent a miniscule amount to run commercials.

But Barnette’s bare-bones campaign received some last-minute help from a group with deep pockets.

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The Club for Growth, the pro-business and anti-tax group that is a major spender in Republican primaries, recently endorsed Barnette and last week announced that it has dished out $2 million to run an ad statewide in Pennsylvania that highlights the candidate’s biography.

And Barnette also recently landed the endorsement of the Susan B. Anthony List, a leading pro-life outside group. SBA List told Fox News on Friday it was spending six-figures to run digital ads in support of Barnette.

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For Trump, the Republican Senate primary is another test of his clout with the GOP. The former president, 16 months removed from the White House, remains the most popular and influential politician in the Republican Party, as he endorses scores of candidates up and down the ballot and repeatedly flirts with making another presidential run in 2024.

Trump scored a big victory two weeks ago in Ohio’s jam-packed and combustible Republican Senate primary, when the candidate he endorsed – former hedge fund executive and best-selling author JD Vance – edged the rest of the field. And a week later, Trump-backed Rep. Alex Mooney of West Virginia topped fellow Republican Rep. David McKinley in a primary battle between two incumbents.

But the same night, Charles Herbster - the candidate Trump endorsed and held a rally on his behalf in Nebraska’s GOP gubernatorial primary – lost, becoming the first of the candidates backed by the former president this year to go down to defeat.

State Sen. Doug Mastriano, a Republican running for governor, meets supporters at a campaign stop, May 10, 2022, in Portersville, Pennsylvania. (AP Photo/Keith Srakocic)

Trump’s sway with Republicans is also on the line in Pennsylvania’s GOP gubernatorial primary. Trump made a late game endorsement on Saturday of state Sen. Doug Mastriano, the polling front-runner.

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Mastriano aimed to try and help overturn Trump's 2020 loss to now-President Biden, and was outside the U.S. Capitol when it was stormed on Jan. 6, 2021, by right-wing extremists aiming to disrupt congressional certification of Biden's Electoral College victory. And both Mastriano and Barnette, who’ve campaigned together, continue to support Trump's unproven claims that the 2020 election was "stolen" due to "massive voter fraud" and agree with the former president's efforts to repeatedly re-litigate his election loss.

Pennsylvania is one of five states to hold primaries on Tuesday, joining North Carolina, Kentucky, Idaho, and Oregon.

Rep. Ted Budd, who is running for the Senate, joins former President Donald Trump at a campaign rally on April 9, 2022, in Selma, North Carolina. (Allison Joyce/Getty Images)

Trump has his best shot of victory in a heavily contested GOP primary on May 17 in North Carolina, where last summer he endorsed Rep. Ted Budd in the state’s open GOP-held Senate seat race. For months, Budd was unable to leverage the former president’s endorsement to boost his poll numbers and fundraising figures. Trump held a rally in North Carolina for Budd in early April, and in recent weeks the congressman surged to front-runner status in the increasingly contentious primary showdown that also includes former Gov. Pat McCrory, and former Rep. Mark Walker.

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But In Idaho, Trump is backing far-right Lt. Gov. Janice McGeachin, who is one of seven primary challengers running against incumbent Republican Gov. Brad Little, whom polling suggests is the clear front-runner.

While Trump did little to help McGeachin, he traveled to the Keystone State to headline a rally with Oz, held two tele-rallies in the final stretch, and recorded the robo-calls.

Senate candidate Mehmet Oz, accompanied by former President Donald Trump, speaks at a campaign rally in Greensburg, Pennsylvania, May 6, 2022. (AP Photo/Gene J. Puskar)

Now, the possibility of Oz losing on the same night has some in Trump world nervous.

"This race in Pennsylvania is much closer than Trump ever thought it would be. And Tuesday is going to be a major blow if Oz isn't the nominee. And that is noticed in Trump world," an adviser to the former president, who asked to remain anonymous to speak more freely, told Fox News.

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The Democratic Senate primary, a much less crowded and combustible showdown than the GOP race, grabbed plenty of attention over the weekend when the overwhelming front-runner – Lt. Gov. John Fetterman – announced on Sunday that he was hospitalized after suffering a stroke. 

Fetterman emphasized that he’s "well on my way to a full recovery" and added that his "campaign isn’t slowing down one bit, and we are still on track to win this primary on Tuesday, and flip this Senate seat in November."