Martha McSally and Kyrsten Sinema during the 2018 Senate campaignMatt York

Not since Abraham Lincoln has a Republican scored a better consolation prize for losing a Senate race.

Last month, Arizona voters rejected Martha McSally in favor of Democrat Kyrsten Sinema after the two waged a hard-fought battle for the Senate seat vacated by the retiring Senator Jeff Flake. Come January, McSally will take a seat in the Senate anyway, serving right alongside the woman who defeated her.

Arizona Governor Doug Ducey on Tuesday said that he will appoint McSally, a former Air Force fighter pilot and two-term member of the House, to serve out the remainder of the late Senator John McCain’s term in Washington. Ducey’s first appointed replacement for McCain, former Senator Jon Kyl, informed the governor that he would be resigning on December 31, reopening the vacancy he filled in September.

Ducey’s selection of McSally was not entirely a surprise—the possibility that she would take McCain’s seat had been a source of speculation in Arizona throughout the final months of the late senator’s life, even as McSally campaigned to win a spot in the upper chamber in her own right. But the appointment so soon after what became an ugly and razor-close election will set up one of the most awkward pairings of senators from the same state in modern history. The Senate Historical Office was searching its records on Tuesday morning to see if two members have ever served together after campaigning against each other the year before. (Lincoln never served in the Senate after losing successive 1856 and 1858 campaigns in Illinois; instead, he ran for—and won—the presidency in 1860.)

The closest example found was from three decades ago in Washington State, where the Republican Slade Gorton lost to the Democrat Brock Adams in 1986, only to win the state’s other Senate seat two years later, says Daniel Holt, an assistant Senate historian. Gorton and Adams served together until 1993. And in 1974, Ohio Democratic Senator Howard Metzenbaum and the Republican Robert Taft Jr. briefly served together four years after they ran against each other.

McSally and Sinema have each served in the state’s congressional delegation for the past four years. But they fought bitterly at times this fall as both sought to become the first woman elected to the Senate from Arizona. During their lone televised debate in October, McSally accused Sinema of “treason” for comments she made during a radio interview in 2003, when she answered a hypothetical question about whether the host should join the Taliban. Sinema “scarcely looked” at McSally during that debate or a second, untelevised matchup the two held days later at the Arizona Republic, the newspaper reported. In November, Sinema defeated McSally by 2.4 percentage points and will become Arizona’s first Democratic senator in more than 20 years.

Adding to the awkwardness on Tuesday was the possibility that McSally would actually be sworn in before Sinema, thereby leapfrogging her in seniority and making history as the state’s first woman senator. Under the Constitution, Sinema will be sworn in on January 3 along with other newly elected members at the start of the 116th Congress. Kyl’s resignation on December 31 leaves open the option for McSally to take office first. Sinema, whose extra two years in the House would give her a tiebreaker in seniority,  probably doesn’t need to worry, however. “Since we are unlikely to be in session between the 31st and the day the new Congress convenes on the 3rd, that question is moot,” says Don Stewart, the spokesman for Senate Majority Leader Mitch McConnell. Ducey told reporters on Tuesday that Sinema would be sworn in first and be Arizona’s senior senator.

McSally and Sinema wouldn’t be the first tandem of same-state senators to have a chilly relationship. Though there’s a perception that senators set aside partisan—and personal—beefs for the good of the state they collectively represent, “that’s a great myth,” said Jim Manley, a former longtime aide to former Democratic Senators Edward Kennedy and Harry Reid. “That’s not always the case by any stretch of the imagination,” he told me, citing examples where even long-serving members of the same party, such as Kennedy and John Kerry in Massachusetts and Chris Dodd and Joe Lieberman in Connecticut, didn’t particularly get along.

While Sinema won a full six-year term, McSally will have to face the voters again in 2020. Her appointment will give her the advantage of incumbency, but Democrats immediately attacked Ducey’s decision to elevate a defeated candidate as following a pattern of Republican legislators and governors flouting the will of voters. “Why appoint a loser when you could find a fresh face with a better shot in 2020?” asks Lauren Passalacqua, a spokeswoman for the Democratic Senatorial Campaign Committee. “That’s the question that will haunt Governor Ducey and the Washington Republicans who installed Martha McSally to a seat she couldn’t earn.”

“Voters rejected her once, and will do so again,” Passalacqua predicts.

McSally stuck close to the political center during her first term in Congress, but she veered right to win her Senate primary and then hugged President Trump during the general-election campaign. The shift irritated McCain allies who were looking for a Republican to honor the late senator’s legacy as a maverick willing, at times, to stand up to his party. Cindy McCain tweeted on Tuesday that she “respected” Ducey’s decision to appoint McSally. “Arizonans will be pulling for her,” she wrote, “hoping that she will follow his example of selfless leadership.”

At a press conference with Ducey on Tuesday, McSally said she looked forward to serving with Sinema. “There’s a lot of common ground between us, and I’m ready to hit it running,” she said. “We had a very spirited campaign, but it’s over.”

Both soon-to-be senators likely have a political incentive to move beyond this year’s campaign. Sinema ran as a moderate despite her past as a liberal Green Party activist, and collaborating with her former rival could be a way to demonstrate that she was sincere.

But after such a bitterly fought campaign and with another election right around the corner, a quick turn to bipartisan bonhomie might be easier said than done. “The politics of the moment are going to demand they try and work together,” Manley told me, before quickly adding: “Having said that, the Senate is going to be nothing but a partisan killing field for the next two years.”

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