“Arizona needs someone who understands the critical issues, who can get to work on Day One and who embodies a spirit of service, of putting the people we represent above all else. Martha McSally possesses these qualities,” Ducey said.

Ducey added that Sinema would be sworn in first and would be the state’s senior senator. Sinema was the first woman elected to represent Arizona in the Senate.

McSally said she was “humbled” and “honored” by the appointment. She praised Sinema, saying she looked forward to working across party lines with the Democratic senator despite the bitter attacks between the two during the campaign, which included McSally accusing Sinema of treason during a contentious debate.

“When I ran for the Senate, it was with a full understanding of the monumental responsibility that comes with that office,” McSally said. “It’s with that same appreciation for this office that I humbly stand before you today.”

Ducey faced a difficult decision on the Senate appointment. In the weeks after McSally’s loss, some Republicans in Arizona and Washington expressed frustration with her for waging what they described as a less-than-stellar 2018 campaign — and some wanted the governor to look elsewhere.

Republicans in Arizona noted that McSally ran far behind Ducey, who coasted to reelection this year. And some were particularly frustrated by a McSally campaign memo that tried to explain away her loss to Sinema, pinning it on external factors like the late primary date, Sinema’s spending advantage and Trump’s lagging approval rating in the state. McSally’s loss was the first by a Republican in an Arizona Senate race since 1988.

Yet other senior Republicans were eager for the congresswoman to get the appointment. McSally has long been viewed as a rising star in the party.

Among those in her corner was Mitch McConnell. The Senate majority leader, who has spoken with Ducey several times since the midterms, privately contended that McSally’s experience running statewide and her fundraising network from this year’s campaign would give her the best opportunity to hold the seat during the 2020 special election. The winner of that race will also have to run for a full term in 2022 after serving out the final two years of McCain’s last term.

In recent weeks, McSally has taken steps to reassure those with lingering doubts. Earlier this month, she met privately with Ducey. And last week, she huddled with McCain’s widow, Cindy. Some in the McCain orbit had been frustrated by McSally’s decision to closely align herself with President Donald Trump as she campaigned for the Senate seat.

“My husband’s greatest legacy was placing service to AZ & USA ahead of his own self-interest. I respect @dougducey’s decision to appoint @RepMcSally to fill the remainder of his term. Arizonans will be pulling for her, hoping that she will follow his example of selfless leadership,” McCain tweeted on Tuesday morning.

Ducey said during the news conference that he was happy McSally met with Cindy McCain to “clear the air” ahead of the appointment.

McSally, who faced criticism during the campaign for not giving due honor to McCain, was effusive in her praise Tuesday. She called McCain a “giant in the Senate, an Arizona icon and an American hero.” She said she would commit to holding herself to McCain’s standard of service.

For his part, Trump congratulated McSally on her appointment Tuesday night, writing on Twitter that she would do “a fantastic job.“

Democrats consider Sinema’s win a harbinger of future victories in fast-changing Arizona, and they are certain to contest the seat aggressively in 2020. Those mentioned as potential candidates include Grant Woods, a former McCain chief of staff and state attorney general who recently became a Democrat; Mark Kelly, an astronaut and the husband of former Rep. Gabby Giffords; Rep. Ruben Gallego; and Rep.-elect Greg Stanton, former mayor of Phoenix, who won Sinema’s seat in November.

Lauren Passalacqua, a spokeswoman for the Democratic Senatorial Campaign Committee, called McSally a “weak candidate” in a statement.

“Why appoint a loser when you could find a fresh face with a better shot in 2020?” Passalacqua said. “That’s the question that will haunt Gov. Ducey and the Washington Republicans who installed Martha McSally to a seat she couldn’t earn.”