The US senator Kyrsten Sinema has switched her political affiliation to independent, leaving the Democratic party just days after it won a Senate race in Georgia to secure a 51st seat in the chamber.

“I have joined the growing numbers of Arizonans who reject party politics by declaring my independence from the broken partisan system in Washington. I registered as an Arizona independent,” she said in an op-ed for Arizona Central, a local media outlet.

In a separate Politico interview published on Friday, Sinema said she would not caucus with the Republican party. If that holds, Democrats could still maintain greater governing control in the closely divided chamber.

Democrats had held the Senate 50-50, with the vice-president, Kamala Harris, holding a tie-breaking vote. Raphael Warnock’s victory in Tuesday’s runoff election in Georgia handed them their 51st seat.

Two other senators – Bernie Sanders of Vermont and Angus King of Maine – are registered as independents but generally caucus with Democrats.

Sinema said her shift came as a growing number of people in her state were also declaring themselves politically independent, rejecting the Republican and Democratic political labels.

“Like a lot of Arizonans, I have never fit perfectly in either national party,”she wrote.

Sinema intends to maintain her committee assignments from the Democrats, an aide told Reuters on condition of anonymity. The aide would not say whether or not Sinema would continue to caucus with Democrats.

The senator herself, however, said she would not caucus with the Republican party, according to an interview published by Politico on Friday.

If that holds, Democrats could still maintain greater governing control in the closely divided chamber.

Sinema and the Democrat Joe Manchin of West Virginia have kept Washington in suspense over the last two years as they repeatedly have withheld their needed votes for legislative initiatives sought by Joe Biden.

At the same time, they have worked in a bipartisan way on high-profile bills that have become law, while forcing compromise.

Sinema was realistic on Friday about the fact that she will get criticism from Democrats for her shock news.

“I’m not worried about folks who may not like my approach, I’m going to continue to do what is right for my state,” she told CNN’s Jake Tapper in an interview that will air in fuller detail on Friday afternoon and Sunday morning.

“I’m doing something that comports with my values,” she said.

The White House press secretary, Karine Jean-Pierre, issued a statement noting that the Democrats will continue to control the Senate.

“We understand that her decision to register as an independent in Arizona does not change the new Democratic majority control of the Senate, and we have every reason to expect that we will continue to work successfully with her,” she said.

Jean-Pierre’s statement also noted: “Senator Sinema has been a key partner on some of the historic legislation President Biden has championed over the last 20 months, from the American Rescue Plan to the Bipartisan Infrastructure Law, from the Inflation Reduction Act to the Chips and Science Act, from the Pact Act to the Gun Safety Act to the Respect for Marriage Act, and more.”

The Pact Act was designed to improve healthcare access and funding for military veterans who were exposed to toxic substances during their service.

Sinema’s departure from the Democratic party is less about frustrating their ability to run the Senate for the next two years, and more about protecting her own position in Arizona, Semafor reported.

She was unpopular enough with Democrats in the state that she was widely expected to face a primary in 2024.

But now that she is out of the party, that primary will not happen. Instead, Democrats are going to face the tough decision of whether to run a candidate against her – and risk splitting their voters and losing the seat to the GOP – or accept that she is their best bet, even if she is not actually in the party.