President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE took a shot at retiring Arizona Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (R) on Wednesday following Rep. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE's (R-Ariz.) victory in the state's GOP Senate primary.

The president tweeted just after midnight Wednesday morning that McSally, who ran on her loyalty to the president, "rejected" an endorsement from Flake in the primary.

"Martha McSally, running in the Arizona Primary for U.S. Senate, was endorsed by rejected Senator Jeff Flake....and turned it down - a first! Now Martha, a great U.S. Military fighter jet pilot and highly respected member of Congress, WINS BIG. Congratulations, and on to November!" Trump wrote.

Martha McSally, running in the Arizona Primary for U.S. Senate, was endorsed by rejected Senator Jeff Flake....and turned it down - a first! Now Martha, a great U.S. Military fighter jet pilot and highly respected member of Congress, WINS BIG. Congratulations, and on to November! — Donald J. Trump (@realDonaldTrump) August 29, 2018

Flake responded just more than an hour later, refuting Trump's claim that he endorsed McSally and adding that his last endorsement was for Alabama Sen. Doug Jones (D), who defeated a Trump-backed GOP challenger, Roy Moore Roy Stewart MooreRoy Moore sues Alabama over COVID-19 restrictions Vulnerable Senate Democrat urges unity: 'Not about what side of the aisle we're on' Sessions hits back at Trump days ahead of Alabama Senate runoff MORE.

"Sorry, @realDonaldTrump. I made no endorsement in this race. I think the last endorsement I made was in the Alabama race," he wrote.

Sorry, @realDonaldTrump. I made no endorsement in this race. I think the last endorsement I made was in the Alabama race.https://t.co/yob5VVNAOe pic.twitter.com/KbzKAGRdDB — Jeff Flake (@JeffFlake) August 29, 2018

McSally handily won Tuesday night's Arizona Senate primary, defeating GOP candidates Kelli Ward and former Sheriff Joe Arpaio, who was pardoned by the president earlier this year after being found in contempt of court over racially motivated traffic stops.

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While Flake did not endorse McSally directly, he did express his desire for the Arizona lawmaker to prevail in the primary in comments to reporters on Tuesday.

“I think McSally will win. I hope she does. That’s the only shot that obviously Republicans have to hold on to the seat, but it’s even difficult then. This is going to be a hard-fought general election,” Flake said.

"I think long term if we don’t appeal to a broader electorate and quit trying to drill down harder on the base and just, you know, give into the politics of anger and resentment, we’re gonna lose big time long term,” he added.