The one constant in Senator Kyrsten Sinema’s political career, from her start as a left-wing rabble rouser and Ralph Nader aide to her announcement on Friday that she was leaving the Democratic Party to become an independent, is her boundless ability to draw attention to herself.
Less than 72 hours after Democrats celebrated winning Georgia’s Senate race and the presumed 51st vote in the chamber, Ms. Sinema yanked the focus of the political world in Washington and Arizona back to her.
This time, it was not another agenda-stymieing disagreement with the party that spent millions electing her to office, but instead a declaration that she was breaking with Democrats entirely, at least in name.
“I’m going to be the same person I’ve always been. That’s who I am,” Ms. Sinema said in a two-minute video on Twitter on Friday morning, adding, “Nothing is going to change for me.”
Democrats believe — or hope — that little will change in Congress, where Ms. Sinema will keep her Democratic committee assignments and where her defection will not change her former party’s control of the Senate.
But in Arizona’s Democratic circles, distaste for the senator runs deep, and her announcement immediately shifted the spotlight to the 2024 race for her Senate seat.
Democrats in the state have long presumed that she would run for re-election and that she was all but certain to face a difficult primary challenge, possibly from Representative Ruben Gallego, who has regularly criticized her over the past two years, or from Representative Greg Stanton, who signaled his interest on Friday. Ms. Sinema, however, left her potential rivals guessing, batting away questions about future bids for office.
Hannah Hurley, a spokeswoman for Ms. Sinema, suggested that the senator had long promised to be an independent voice for the state, citing an ad from her 2018 campaign that emphasized a “fiercely independent record” and a “reputation for working across the aisle.”
“Independent, just like Arizona,” the spot said.
“She is not focused at all on campaign politics,” Ms. Hurley said of Ms. Sinema, who declined an interview on Friday afternoon.
Democrats in Arizona signaled on Friday that they still planned to support a candidate against Ms. Sinema, whether it ends up being Mr. Gallego, Mr. Stanton or someone else. National Democratic leaders were cagey on Friday about how they would approach the 2024 race or a potential independent Sinema campaign. One main worry for Democrats is that running a strong candidate against Ms. Sinema in the general election might inadvertently help elect a Republican.
Representatives for Senate Democrats’ campaign arm and for Senate Majority PAC, the leading Democratic super PAC devoted to Senate races, declined to comment on Friday afternoon about Ms. Sinema’s move. Senator Chuck Schumer, the New York Democrat and majority leader, said that Ms. Sinema would keep her committee positions. “Kyrsten is independent,” he said in a statement. “That’s how she’s always been.”
And the White House press secretary, Karine Jean-Pierre, said in a statement that President Biden expected to “continue to work successfully” with Ms. Sinema but did not address her 2024 prospects.
Ms. Sinema was elected to the Senate in 2018, filling the seat of another party apostate, Senator Jeff Flake, a Republican who declined to seek re-election after breaking with President Donald J. Trump. He is now Mr. Biden’s ambassador to Turkey.
The working assumption in Arizona political circles has long been that progressive anger at Ms. Sinema was concentrated among Democratic political activists, and that she could survive a primary from her left. But recent polling suggests that she has lost the confidence of many Arizona voters outside the center-right Chamber of Commerce types whom she has cultivated with the latest iteration of her political identity.
A Civiqs survey conducted shortly before Election Day found she had an approval rating of just 7 percent among the state’s Democrats, 27 percent among Republicans and 29 percent among independents.
Moderate Republicans uncomfortable with Mr. Trump’s politics have turned Arizona from a red state into a political battleground, swinging to Mr. Biden in 2020 and helping Democrats triumph in statewide elections last month against a Trump-backed slate of candidates. Ms. Sinema’s calculation in leaving the Democratic Party is that those voters can lift her to victory on their own.
The Trumpian makeover of the Arizona Republican Party has also alarmed Democrats who want their candidates to be a forceful opposition — not present themselves as ideologically ambiguous.
“Everything she’s done has been in the service of Kyrsten Sinema,” said Ian Danley, a progressive political consultant in Phoenix. “There’s really no other way to describe the decisions she makes. She cares about attention. She cares about setting herself up for the next thing.”
The Democratic grumbling has Mr. Gallego and Mr. Stanton leaving little pretense about their ambitions to challenge Ms. Sinema in 2024. Mr. Gallego, a Harvard graduate and Marine veteran, has been a regular presence on cable news whenever Ms. Sinema alienates the party base, and his lively and occasionally profane Twitter feed often criticizes her. On Friday, he called her decision a “betrayal” of volunteers who knocked on doors in triple-digit heat to elect her as a Democrat.
Mr. Stanton, a former Phoenix mayor who holds Ms. Sinema’s old House seat, on Friday tweeted what appeared to be a snapshot of a poll showing him leading Ms. Sinema by 40 percentage points in a hypothetical matchup.
Her decision, he wrote, “isn’t about a post-partisan epiphany. It’s about political preservation.”
Arizona’s progressive organizations and officials were already wary of Ms. Sinema during her 2018 run for Senate, but at the time no Democrat in the state had won election to the chamber in three decades. They collectively held their noses to turn out the vote for her in hopes that she would reciprocate their support once in office.
Once Ms. Sinema became the linchpin of Senate Democrats’ narrow governing majority in 2021, those groups began publicly fuming at Ms. Sinema, whom they accused of abandoning her promises on immigration, health care and the environment. Ms. Sinema dismissed their complaints, echoing her general practice of dodging journalists in Washington and Arizona.
When she theatrically turned a thumbs-down on a Senate vote in March 2021 to increase the minimum wage to $15 per hour, it was the last straw for her party’s base. When she skipped votes to participate in Ironman triathlons or spent weeks as an intern at a Sonoma County winery, it served only to cement her reputation among progressives that she had removed herself from the concerns of working-class Arizonans.
In the fall of 2021, activists from LUCHA, one of the groups that worked to elect Ms. Sinema, confronted her at Arizona State University. Activists followed Ms. Sinema into a bathroom and demanded that she explain why she had not done more to push for a pathway to citizenship for about eight million undocumented immigrants. The protesters said they had taken the drastic action only because Ms. Sinema did not hold town-hall meetings or answer calls from constituents. Protesters have also chased her through airports and followed her into a high-priced fund-raising event at an upscale resort.
“We are not surprised that she would once again center herself,” said Alejandra Gomez, the executive director of LUCHA. “This is another unfortunate, selfish act. It is yet another betrayal — there have been a slew of betrayals, but this is one of the ultimates, because voters elected her as Democrat, and she turned her back on those voters.”
But some of Ms. Sinema’s allies argue that she has been consistently clear about having an independent streak.
“I love that she’s going to be even freer now to just do the right thing,” said Tammy Caputi, a Scottsdale City Council member who is herself a political independent, adding that Ms. Sinema had long been leery of being “straitjacketed by partisan politics.”
She went on, “I’m hoping that Kyrsten’s decision to become an independent will spark other people to think long and hard about being overly attached to one party.”
But for many Arizonans and Ms. Sinema’s fellow senators, the big question is whether or not she will run again in 2024, which she neglected to clarify in her video announcement, an op-ed article in The Arizona Republic or news media interviews that were released on Friday morning. Because she keeps a tight political circle of advisers and speaks little to the news media, there has long been far more speculation than explanation about her motivations.
“Anybody that underestimates Senator Sinema is being foolish,” said Representative Raúl Grijalva, a liberal Arizona Democrat who said he planned to support Mr. Gallego if he ran. “She’s going to be formidable if she decides to run.”
A person familiar with Mr. Stanton’s deliberations confirmed that he was considering running for Senate in Arizona in 2024 as a Democrat. The person confirmed that the image from a poll that Mr. Stanton tweeted on Friday was from a statewide survey in which he had tested his potential candidacy for Senate.
In an interview on Friday, Mr. Gallego said Ms. Sinema’s rush to announce her party switch soon after the outcome of the Georgia race fit neatly into her career trajectory.
“I wish she would have waited for the Democrats at least to enjoy a couple more days after the victory,” he said. “But, you know, she’s not known really for thinking of others.”
Mr. Gallego said he would make a decision about what office to seek in 2024 in the new year. He had just gotten off the phone with his mother, who was catching up on the news.
“She said: ‘I heard Sinema is not running. Make sure to talk to me before you do anything,’” Mr. Gallego said.