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Sen. Kyrsten Sinema has announced that she will leave Congress at the end of her term this year. She was elected as a Democrat but left the party to become an Independent in 2022.Anna Moneymaker/Getty Images

Independent U.S. Senator Kyrsten Sinema of Arizona said on Tuesday that she will not run for re-election in the highly competitive state, which will be critical to her former Democratic Party’s chances of maintaining its narrow majority.

Sinema’s decision clears the way for an expected head-to-head contest in the November 2024 election between Democratic Representative Ruben Gallego, a former Marine veteran who served in Iraq, and Kari Lake, a far-right Republican who lost a bid for Arizona governor in 2022.

Sinema, 47, was elected in 2018 as a Democrat, but drew her party’s ire after she foiled some policy proposals of President Joe Biden along with moderate Democratic Senator Joe Manchin. They most notably refused to support any change to the Senate’s filibuster rule to allow Democrats to enact major voting rights legislation.

At the same time, Sinema, the first openly bisexual senator, gained the respect of many of her Senate colleagues as a dogged legislator who was willing to plunge into difficult issues until compromises were reached.

Notably, Sinema was a key negotiator on Biden’s successful $1 trillion infrastructure investment bill that was enacted in 2021. Just this year, she was one of three main negotiators on one of the most important border security and immigration reform bills offered in the Senate in a decade – which was promptly killed by former President Donald Trump’s opposition that led to the collapse of Republican support.

Following her clashes with fellow-Democrats, Sinema changed her party affiliation to independent in December 2022. She continued caucusing with the Democrats in their 51-49 majority, although she said in subsequent media interviews that she rarely attended caucus meetings even before she formally left the party.

She blamed an increasingly partisan tone of U.S. politics for her decision to leave office.

“Because I choose civility, understanding, listening, working together to get stuff done I will leave the Senate at the end of this year,” Sinema said in a video posted on X. “Compromise is a dirty word.”

Her move came as Americans in more than a dozen states cast ballots in Super Tuesday primary elections, with Trump seeking to strike a knockout blow in his run for the Republican nomination to challenge Biden in November.

Sinema’s announcement came the week after Republican Leader Mitch McConnell, who has represented Kentucky in the Senate since 1985, said he will retire from his leadership role at year’s end following a record-long run.

Arizona’s races have become among the closest-watched – and most expensive – in the country in recent years. The Senate race between Democratic Senator Mark Kelly and Republican challenger Blake Masters in 2022 saw $129 million spent. Kelly won re-election with 51.4% of the vote.

“I want to thank Senator Sinema for her nearly two decades of service to our state,” Gallego said in a statement issued immediately after her announcement in which he called for her support.

Besides the spirited race expected in Arizona, Democrats have a difficult road ahead in keeping their Senate majority. Incumbent Democrats are trying to hold onto seats in states that likely will see furious battles in the presidential race as well. Longtime Senators Bob Casey and Sherrod Brown could face tough re-election bids in Pennsylvania and Ohio.

The Democrats’ seat in West Virginia, where Manchin announced in November he would not be running for re-election, is all but certain to be captured by Republicans. And there are new worries in Maryland, where Democrat Ben Cardin is retiring and a popular former Republican governor, Larry Hogan, is running to replace him.

Lake, a former television news anchor, ran in 2022 for governor, narrowly losing to Democrat Katie Hobbs. The Republican still has not conceded defeat, following Trump’s practice of claiming falsely that his 2020 presidential election loss was the result of widespread voting fraud.

“Senator Sinema had the courage to stand tall against the Far-Left in defense of the filibuster,” Lake wrote on X.

Whatever the outcome of November’s Senate elections, one thing is certain. There will be far less fashion on the Senate floor when Sinema exits with her brightly coloured wardrobe that enlivened members’ famously drab dress.

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