Senator Kyrsten Sinema of Arizona, the Democrat turned independent who cut bipartisan deals that cemented parts of President Biden’s agenda but also stymied some of her former party’s highest priorities, said on Tuesday that she would not seek re-election.
Her announcement ended a year of speculation about her future in a politically competitive state. It cleared the field for a traditional matchup in the high-stakes battle for control of the Senate, between a more conventional Democrat, Representative Ruben Gallego, and the eventual Republican nominee.
“Because I choose civility, understanding, listening, working together to get stuff done, I will leave the Senate at the end of this year,” she said in a video announcement.
Ms. Sinema, a first-term senator who left the Democratic Party in 2022, faced potentially long odds in a three-way race for re-election as Democrats fight to maintain control of the Senate. Recent polling found her trailing both Mr. Gallego and Kari Lake, the favorite for the Republican nomination who is an acolyte of former President Donald J. Trump and has championed his baseless election fraud claims.
Her decision to bow out now set up a more direct showdown, likely between Mr. Gallego and Ms. Lake — though Mark Lamb, a sheriff, is also seeking the Republican nomination.
Senator Steve Daines of Montana, who heads Republicans’ Senate campaign committee, argued that Ms. Sinema’s decision not to run would boost Ms. Lake, who is endorsed by his National Republican Senatorial Committee.
“With recent polling showing Kyrsten Sinema pulling far more Republican voters than Democrat voters, her decision to retire improves Kari Lake’s opportunity to flip this seat,” Mr. Daines said in a statement.
But Stan Barnes, a former Republican legislator and lobbyist for Copper State Consulting Group, a Phoenix-based firm, said the advantage would go to the Democrats, whose votes might otherwise have been split between Ms. Sinema and Mr. Gallego.
“When it comes to the U.S. Senate in Arizona, Democrats are mostly unified and Republicans are decidedly fractured,” Mr. Barnes said. “This means: advantage Gallego.”
In a statement, Mr. Gallego kept his focus on criticizing Ms. Lake, while thanking Ms. Sinema for her service to Arizona.
“Democrats, independents and Republicans alike are coming together and rejecting Kari Lake and her dangerous positions,” he said.
Ms. Lake, who was in Washington on Tuesday for a fund-raiser, spoke at length to reporters in the Capitol, seeking to praise Ms. Sinema and saying that the senator’s exit from the race may make her own bid “a little bit easier.”
“I respect Kyrsten Sinema as a human being,” Ms. Lake said. “While I disagree with her on almost all of her policy, I have great appreciation for the courage she showed when it came to protecting the filibuster.”
Ms. Sinema continued to align with Democrats after leaving the party, maintaining her committee seats and providing decisive votes for key parts of Mr. Biden’s agenda. She stood by Democrats on most social policies and supported Mr. Biden’s judicial nominees. But she also angered leaders of her former party by opposing major Democratic priorities, including efforts to raise taxes on corporations and attempts to weaken the filibuster to push through major voting legislation, among other policies.
In a statement on Tuesday, Senator Chuck Schumer, Democrat of New York and the majority leader, said Ms. Sinema had “blazed a trail of accomplishments in the Senate,” citing her work on Mr. Biden’s Inflation Reduction Act, his major infrastructure law and a law mandating federal recognition for same-sex marriages.
Ms. Sinema took pride in her relationships with centrist Republicans. She played a critical role in brokering a breakthrough bipartisan package earlier this year to clamp down on migration across the United States border with Mexico while providing fresh aid to Ukraine and other U.S. allies — a bill that Republicans demanded and then quickly tanked.
In the wake of its demise, Ms. Sinema appeared disillusioned and angry, having watched some of the Republicans she had worked closely with in cutting the deal swiftly turn against it.
“Turns out they want all talk and no action,” she said of Republicans in a scathing speech on the Senate floor just before the package failed. “It turns out border security is not actually a risk to our national security; it is just a talking point for the election.”
“When we work together, we can solve problems,” she added later. “We did that here. And you decided no.”
In her statement on Tuesday, she emphasized how frustrated she had become about the state of American politics.
“These solutions are considered failures, either because they’re too much or not nearly enough,” Ms. Sinema said, adding: “Compromise is a dirty word. We’ve arrived at that crossroad, and we chose anger and division. I believe in my approach, but it’s not what America wants right now.”
After winning a close 2018 contest over Martha McSally, a Republican, to become Arizona’s first elected female senator, Ms. Sinema has had an eventful tenure in Washington as an enigmatic figure who often kept colleagues guessing about her intentions and defied convention.
Her emphatic thumbs-down of an effort in 2021 to raise the minimum wage infuriated progressives; protesters have chased her through airports; and activists have criticized what they say is her eagerness to side with business interests over the campaign promises she made to Arizona voters. Arizona Democrats censured her after she refused to agree to change filibuster rules to pass voting rights legislation.
Ms. Sinema’s decision to step aside effectively wipes out the last remaining Democratic-aligned member of the Senate opposed to changing the filibuster, after Senator Joe Manchin III, the conservative-leaning West Virginia Democrat, announced in the fall that he would not seek re-election.
As the deadline for Ms. Sinema to declare her re-election campaign approached in recent months, rumors swirled in Arizona about whether she would do so. Texts from friends and some moderate Republicans who were eager to endorse her went unanswered or were brushed off, leading many to speculate that she would ultimately choose not to run.
Without the support of the Democratic base, Ms. Sinema would have faced an extraordinarily uphill path to re-election, in which she would likely have needed to cobble together a coalition of moderate Democrats, anti-Trump Republicans and unaffiliated independent voters.
She also faced a daunting deadline: To run as an independent candidate, she needed to file more than 42,000 valid signatures by April 1, an expensive and time-consuming endeavor even for a candidate with $10.6 million on hand, as Ms. Sinema reported in recent campaign finance filings.
She never filed a statement of interest with the secretary of state’s office, a required step before beginning to gather signatures.
Robert Jimison contributed reporting.
