Washington(CNN) President Donald Trump and White House officials have had a series of conversations with prospective Republican candidates about challenging Arizona GOP Sen. Jeff Flake in the 2018 primary.

Kelli Ward, who has already launched her campaign, and Robert Graham, a former state GOP chair and Trump adviser who is considering it, both told CNN on Monday they have had multiple conversations with White House officials about opposing Flake in the Senate primary.

Graham said the talks began shortly after the 2016 presidential campaign concluded, and both Graham and Ward said further conversations took place as recently as two weeks ago.

Another potential candidate -- state treasurer Jeff DeWit -- has had multiple conversations with Trump, sources familiar with those talks said. DeWit is close with Graham, making it unlikely both would run.

Trump was furious at Flake last fall when the Arizona senator called on Trump to withdraw from the presidential race after the emergence of the "Access Hollywood" tape.

He told a small group of Arizona Republicans last fall -- including Graham -- that he would spend $10 million on defeating Flake in the 2018 Senate primary, a source familiar with the conversation confirmed. That conversation and the White House's further involvement in recruiting a primary challenger were first reported Monday by Politico's Alex Isenstadt.

"They used Jeff Flake in Hillary Clinton's ads, for heaven's sakes. It was like pouring salt on the wounds," Graham told CNN.

"I don't think that that relationship has been mended, even though Jeff Flake is using Donald Trump's name in some of his fundraising emails," Ward said in a separate interview.

Flake campaign manager Josh Daniels told CNN that the campaign is "Not going to speculate on speculation."

"The only thing Sen. Flake concerns himself with is doing the job Arizonans expect him to," Daniels said. "The rest will take care of itself."

CNN has reached out to the White House for comment and has not yet received a response.

Polls commissioned by Republicans, sources familiar with the data said, have shown that Trump's popularity among Arizona GOP primary voters is still at or near 90%, while Flake's numbers are much lower -- fueling donor interest in ousting Flake.

"The donor community has really come to life in terms of recruitment," Graham said.

Ward would not say whether she has spoken directly with Trump, saying she wants to "keep my conversations private." But, she said, "I do know that I have a lot of support in Arizona and in Washington, DC."

"I think a lot of people had election 2016 fatigue, but I think that they are awakening from that fatigue and are ready to put their money behind the candidate that they believe can actually do the work they want done," she said, calling Flake "such a disappointment."

David Bossie, Trump's deputy campaign manager and the head of Citizens United, a conservative nonprofit organization, told Graham outside a Republican National Committee meeting in San Diego in May that he or DeWit would get a major injection of outside cash if one were to take on Flake, sources familiar with those conversations said.

The Trump-aligned super PAC America First Action announced, but later withdrew, a major advertising buy against Nevada Republican Sen. Dean Heller when Heller crossed Trump by announcing his opposition to the Senate Republican health care bill. The group has not begun discussing financially backing a Flake challenger, a spokeswoman for the group said.

Flake has broken with Trump on several high-profile issues since the election -- including the President's positions on pulling back on ties to Cuba, the North American Free Trade Agreement and the travel ban.

He also publicly said Trump did not have an "acceptable rationale" for firing FBI Director James Comey.

Those positions, Republican sources said, have fueled a fear in the White House and among Republicans supportive of Trump that Flake could be emboldened by winning another six-year term and would become a thorn in Trump's side for the duration of his presidency.