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.) congratulated Rep. Kyrsten Sinema (D-Ariz.) late Monday for winning the race to take his U.S. Senate seat, telling her she will "be great."

"Congratulations to @kyrstensinema on a race well run, and won. It’s been a wonderful honor representing Arizona in the Senate. You’ll be great," Flake wrote in a tweet.

Congratulations to @kyrstensinema on a race well run, and won. It’s been a wonderful honor representing Arizona in the Senate. You’ll be great. — Jeff Flake (@JeffFlake) November 12, 2018

Flake's congratulatory message came after The Associated Press called the tight Senate race between Sinema and 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 favor of the Democrat. She led by a margin of 38,197 votes when the AP called the race Monday.

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In a separate tweet, Flake wrote that McSally had "done Arizona proud" after she posted what Flake described as a "gracious concession speech."

McSally said in her concession speech, which was posted to Twitter, that she wishes Sinema "all success."

"I just called Kyrsten Sinema and congratulated her on becoming Arizona's first female senator after a hard-fought battle. I wish her all success as she represents Arizona in the Senate," McSally said.

Congrats to @kyrstensinema. I wish her success. I’m grateful to all those who supported me in this journey. I’m inspired by Arizonans’ spirit and our state’s best days are ahead of us. pic.twitter.com/tw0uKgi3oO — McSally For Senate (@MarthaMcSally) November 12, 2018

There is a chance that McSally could still end up in the Senate.

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Sen. Jon Kyl (R-Ariz.), who was appointed to Sen. John McCain John Sidney McCainThe Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' Cindy McCain: Trump allegedly calling war dead 'losers' was 'pretty much' last straw before Biden endorsement MORE's seat after McCain's death, has indicated he may not want to continue serving beyond this Congress. That could open the door to Arizona's Republican governor appointing McSally to fill that seat.

With Arizona's race called, Republicans now hold a 51-47 majority in the Senate, with two races yet to be determined.

A recount is underway in Florida's Senate race, where Gov. Rick Scott (R) holds a lead over incumbent Sen. Bill Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE (D). In Mississippi, Sen. Cindy Hyde-Smith (R) will face former Agriculture Secretary Mike Espy (D) in a runoff next month.

If Republicans take both, they would expand their majority in the next Senate by two seats.