Retiring 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 Tuesday backed 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.) in her bid to replace him, hours before polls were set to close in her Republican Senate primary.

“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 told reporters.

Flake continued on AZ primary: "...and 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.” — Jason Donner (@jason_donner) August 28, 2018

Flake, a vocal critic of 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 who announced last fall that he would retire after this Congress, offered his support for McSally as she pushed to pull out a win in Tuesday's Senate GOP primary.

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McSally is facing off against two conservative firebrands, former state Sen. Kelli Ward and former Maricopa County Sheriff Joe Arpaio, for a chance to compete in the November general election for the seat being vacated by Flake.

All three candidates competing in Tuesday's Republican primary have tried to tie themselves closely to Trump, who has relationships with each of the candidates.

Trump has declined to offer an endorsement in the race, though Sen. Cory Gardner Cory Scott GardnerBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Cook Political Report shifts Colorado Senate race toward Democrat MORE (R-Colo.), the head of the National Republican Senatorial Committee, reportedly asked the president to back McSally in a recent phone call.

Ward has garnered negative headlines in recent days over her criticism of the late Sen. John McCain John Sidney McCainAnalysis: Biden victory, Democratic sweep would bring biggest boost to economy The Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ariz.), while Arpaio was pardoned by Trump after being convicted of contempt of court for refusing to end racial profiling of Hispanics during immigration arrests.

The winner of Tuesday's GOP primary is likely to face Democratic Rep. Kyrsten Sinema (Ariz.) in the fall. The three-term congresswoman is well-funded and has avoided a grueling and bitter primary.

A compilation of polls by RealClearPolitics shows Sinema leading all three GOP candidates in hypothetical matchups, but defeating McSally by the smallest margin of the three.

The nonpartisan Cook Political Report lists the Senate race as a “toss up.”