A host of Ohio state and county GOP officials Thursday are drafting a letter urging former President Donald Trump not to endorse in the state's Republican Senate primary, amid a report he plans to back candidate J.D. Vance, multiple Republican sources tell Fox News Digital.

The Ohio GOP Central Committee and about half of the Republican state county chairs are behind the letter, according to the sources. The genesis of the effort came from the campaigns for GOP candidates Jane Timken and Josh Mandel, who fought hard against Trump endorsing Vance, GOP sources say. A GOP source also says the campaign of GOP candidate Mike Gibbons played a role. 

The letter, which Fox News obtained from a source affiliated with one of the GOP Senate campaigns, takes aim at Vance's opposition to Trump ahead of the 2016 presidential election. "We do not support JD Vance for the aforementioned reasons and would urge you not to endorse anyone in this race," the letter to Trump states.

The letter comes after NBC News reported Thursday Trump is expected to endorse "Hillbilly Elegy" author and venture capitalist J.D. Vance. Fox News has not yet confirmed Trump's planned endorsement.

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Former President Donald Trump speaks at Trump National Golf Club in Bedminster, N.J., Wednesday, July 7, 2021.  (AP Photo/Seth Wenig)

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"While we were working hard in Ohio to support you and Make America Great Again, JD Vance was actively working against your candidacy," the letter says regarding 2016. "He referred to your supporters as ‘racists’ and proudly voted for Evan McMullin in 2016. Importantly, JD Vance is not, and has never been a registered Republican. To have someone who has not voted in a Republican primary carrying the mantel for the party is troubling."

A GOP source with knowledge of the discussions told Fox News that Trump called around to donors and advisers in recent days asking their opinions about endorsing Vance. The campaigns of rivals Jane Timken and Josh Mandel pushed back hard against that, the source said. 

"Failing campaigns sometimes band together," a source close to the Vance campaign said Thursday in response to the letter. 

JD Vance, at the Conservative Political Action Conference (CPAC), speaks with Fox News, on Feb. 26, 2022 in Orlando, Florida. (Fox News )

The source close to the Vance campaign also said that it is "surprising that they don't know that Donald Trump actually knows" what Vance said about Trump in the past, as the candidate has been forward about his change in mind. To imply otherwise, the source said, is "insulting." 

"President Trump would be making a fantastic choice by endorsing JD Vance," Marshall Pitchfurd, chairman of the board of Ohio Right to Life, which just endorsed Vance last week, told Fox News Digital. "JD is 100% pro-life without exceptions. He will continue President Trump’s pro-life victories in the US Senate."

Former Ohio GOP State Central Committee Member Ann Becker, meanwhile, said "the last time President Trump endorsed Jane Timken for party chair she stabbed him in the back by supporting Anthony [Gonzalez's] impeachment vote." Timken initially did not condemn Rep. Anthony Gonzalez, R-Ohio, for voting to impeach Trump, though she later did. 

"If Jane and Bob Paduchik worked as hard at getting people to their events as they did getting her endorsers to sign this letter she wouldn’t be in last place," Becker also said. 

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Vance, as well Timken, Mandel, and Gibbons, have long been working to land Trump’s endorsement. And top allies of the former president, including former Trump White House and campaign figures, are supporting or working for the various campaigns.

JD Vance, co-founder of Narya Capital Management LLC and U.S. Republican Senate candidate for Ohio (Gaelen Morse/Bloomberg via Getty Images)

A super PAC backing Vance was infused with a massive $10 million contribution last year by PayPal co-founder, billionaire venture capitalist and Trump ally Peter Thiel — who is also Vance’s old boss. Trump campaign pollster Tony Fabrizio is doing surveys for Vance’s Senate bid and Trump campaign veteran Andy Surabian is a senior adviser on Vance’s team. And Trump ally and Turning Point USA founder Charlie Kirk is backing Vance.

Bill Stepien, who served as Trump’s campaign manager during the summer and autumn of 2020, Justin Clark, who served as deputy campaign manager under Stepien, and Mike Biundo, a top adviser on Trump’s 2016 campaign, are all senior advisers for Gibbons.

Kellyanne Conway, who steered Trump’s 2016 general election campaign and served as a senior counselor in the Trump White House, Corey Lewandowski, who managed Trump’s 2016 campaign during the primaries and who was a key adviser on the 2020 reelection, and Trump campaign veteran and ally David Bossie, are all senior advisers for Timken’s campaign.

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Retired Gen. Michael Flynn, who served as Trump’s first national security adviser, is backing Mandel, as is David Friedman, who served as ambassador to Israel during the Trump administration.

Sniping among the candidates over their loyalty to Trump dates back to February of last year, when Mandel and Timken — the first two major contenders to enter the race — started trying to outdo one another in spotlighting their Trump credentials.

A month later, Trump quizzed Mandel, Timken, Gibbons and Cleveland-based businessman and luxury auto dealership giant Bernie Moreno (who suspended his campaign earlier this year) about their support in a private meeting with the four candidates ahead of a fundraiser at his golf course in Palm Beach, Florida.

The GOP primary is May 3. The winner of the primary will likely face Rep. Tim Ryan, D-Ohio, in the general election.