(Bloomberg) -- Independent Senator Kyrsten Sinema of Arizona said she won’t run for a second term, ending prospects for a turbulent three-way race in one of the nation’s most politically competitive states.

Sinema, who switched her party affiliation from Democrat to independent in 2022, was trailing in third place in polls and her fundraising has been anemic. She criticized partisan dysfunction in Congress in announcing her much-anticipated decision.

“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 statement. 

Sinema, 47, spent months working to secure a recent failed border deal with Republican senators that would have cracked down on illegal border crossings, made it harder to apply for asylum and speed up deportations of undocumented migrants. Republicans then repudiated the deal after Donald Trump criticized it.

The first openly bisexual member of the Senate, she hewed to Arizona’s history of elected moderates and mavericks like the late Republican Senator John McCain. She usually votes with Democrats and supplied crucial support for some of President Joe Biden’s signature legislative achievements but infuriated progressives by blocking key agenda items.

A competitive athlete who runs marathons and triathlons, she faced the prospect of a losing race for reelection.

Her decision follows lackluster fundraising during the final three months of 2023, bringing in less than $600,000 and a fraction of the amounts raised by Republican firebrand Kari Lake and progressive Democratic Representative Ruben Gallego, the favorites for their parties’ nominations.

The announcement sets up a race between Lake, who refused to concede her loss in Arizona’s 2022 gubernatorial race, and Gallego, a military veteran who has been in the House since 2015.

An Emerson College Polling/The Hill survey conducted last month showed Gallego maintaining and possibly enlarging his lead in a two-person contest against Lake. Gallego led by 7 percentage points in a hypothetical two-way contest, up from 6 points in a three-way race. The margin of error was 3 points.

While Sinema attracts more Republicans than Democrats, more than half of her supporters are independents. The Emerson poll shows her independent supporters overwhelmingly shift to Gallego in a two-person race.

Arizona’s voter registration is nearly evenly split between Republicans, Democrats and independents, although Democrats are slightly outnumbered.

Gallego applauded Sinema’s years of public service in a response to her announcement, saying he would welcome her to “join” his efforts in the coming election.

“Protecting abortion access, tackling housing affordability, securing our water supply, defending our democracy — all of this and more is on the line,” Gallego said.

Minutes after her announcement, Gallego’s campaign sent out a fundraising appeal declaring the Senate contest a two-person race.

Earlier: Sinema Breaks From Democrats But Lets Them Keep Senate Grip

Lake, who happened to be visiting Republican senators at the Capitol Tuesday, made her own appeal to win the votes of Sinema’s supporters soon after the announcement. 

“Senator Sinema had the courage to stand tall against the Far-Left in defense of the filibuster — despite the overwhelming pressure from the radicals in her party,” she said on the social media platform X.

Sinema angered many Arizona Democrats and progressives nationally by defending the filibuster and opposing a $15-per-hour minimum wage. She forced Democrats to drop from their signature climate package a “carried-interest loophole” that would have imposed more taxes on private equity managers.

She was censured by the state Democratic party in January 2022 over her refusal to do away with the filibuster to force through voting rights legislation.

But she helped negotiate a string of 2022 bipartisan victories, including Biden’s bipartisan infrastructure law, legislation protecting same-sex marriage and the first significant gun control measure in many years.

Her reelection bid attracted support from donors including Pershing Square Capital Management’s Bill Ackman, actor Sylvester Stallone and real estate developer Harlan Crow.

--With assistance from Erik Wasson, Steven T. Dennis, Bill Allison and Gregory Korte.

(Updates with additional polling, donor, background detail, beginning with fifth paragraph)

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