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-Ariz.) on Wednesday took a swipe at 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 after the president suggested 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 (R-Ariz.) overcame Flake's endorsement to win her primary on Tuesday night.

"Sorry, @realDonaldTrump. I made no endorsement in this race. I think the last endorsement I made was in the Alabama race," Flake said, referencing his support of Sen. Doug Jones (D-Ala.).

Flake attached a photo of a check he donated to Jones's campaign. Flake broke with Trump, who backed former judge 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 in the race despite allegations of sexual misconduct.

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

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Flake did not formally endorse McSally in the GOP primary in Arizona, where three candidates vied for the chance to replace him in the Senate. He told reporters he "hoped" McSally would win, arguing she represented the best chance at victory in November.

Trump wrote in a tweet congratulating McSally on her victory that she turned down Flake's endorsement.

"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 tweeted.

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, who announced last October he intended to retire at the end of his term, has been one of Trump's most outspoken Republican critics, prompting speculation he may challenge Trump in a Republican primary in 2020.

Flake has not ruled out a potential presidential run.