The Arizona Republican Party is opening its doors to Senate candidate Kelli Ward, who is challenging Sen. Jeff Flake for the party's 2018 primary and appeared to receive President Trump's endorsement on Thursday.

The Republican National Committee overseen by Trump is prohibited by GOP rules from intervening in party primaries, either for or against incumbents, except under extraordinary circumstances. But RNC state affiliates have the option of blocking primary challengers from accessing the national party's vast data analytics infrastructure.

The Arizona GOP has chosen to grant Ward access to RNC voter data as Trump prepares to visit Phoenix on Tuesday, where he could formalize an endorsement of Ward.

"Any primary candidate that jumps in will have access," Arizona Republican Party spokesman Torunn Sinclair said of next year's Aug. 28 GOP Senate primary. After this story posted, Sinclair contacted the Washington Examiner and stressed that the state party was remaining neutral in the primary.

Trump and Flake are engaged in a simmering feud that was reignited with the summer publication of a book written by the senator in which he heavily criticizes the president.

Trump on Thursday morning hammered Flake in a Tweet on the heels of enduring a barrage of criticism for his handling of events in Charlottesville, Va. Flake was hardly the only Republican to admonish the president, and indeed he voted for the Senate GOP healthcare bill that collapsed when it fell one vote short of passage.

But Trump is still smarting from Flake's refusal to endorse him in the 2016 presidential race and the senator's renewed complaints about the president's conduct in his book, Conscience of a Conservative: A Rejection of Destructive Politics and a Return to Principle. He's threatened in the past to spend his own money to oust Flake in a primary, and it looks like he might have settled on Ward, a flawed candidate who has run and lost before.

"Great to see that Dr. Kelli Ward is running against Flake Jeff Flake, who is WEAK on borders, crime and a non-factor in Senate. He's toxic!" Trump tweeted. The White House did not respond to an email asking if the tweet should be considered a formal endorsement.

Ward welcomed the president's support and used it as an opportunity to pump her online donor list for donations. "President Trump just gave our campaign a huge boost," she wrote in an email appeal. Flake's campaign spokesman, William Allison, responded to Trump's tweet with a curt statement. "You don't serve Arizona by cutting backroom deals in Washington, D.C. That's why Senator Flake will always fight for the people of our state."

Flake's allies reacted quickly and forcefully, vowing to provide the senator the resources he needs to win re-nomination and succeed in what could be a competitive general election, possibly against Democratic Rep. Kyrsten Sinema.

The NRSC, the Senate GOP campaign arm, and Senate Leadership Fund, the super PAC affiliated with Senate Majority Leader Mitch McConnell, R-Ky., are lining up behind Flake, with more groups likely to join them in the months ahead.

"Jeff Flake is an excellent Senator and a tireless advocate for Arizona and our nation. He has my full support," McConnell said in a statement.

"The NRSC unequivocally supports Senator Flake in his reelection bid," added Sen. Cory Gardner of Colorado, the NRSC chairman.

The Democrats have few opportunities to pick up seats in the midterm, with Arizona and Nevada their only two obvious targets as they play defense in as many as 10 states that Trump won last November.