Sen. Kyrsten Sinema of Arizona has left the Democratic Party and registered as an independent.

Sen. Kyrsten Sinema, a Democrat from Arizona, declared on Friday that she is registered as an independent but will not join the Republican caucus, ensuring that Democrats will maintain their slim Senate majority.

Sinema said she was “declaring my independence from the broken partisan system in Washington.” She has based her political strategy on the renegade approach of the late Sen. John McCain, R-Ariz., and has occasionally irritated Democratic colleagues with her overtures to Republicans and opposition to Democratic priorities.

“I know some people might be surprised by this, but it actually makes a lot of sense,” Sinema told CNN on Thursday. “I’ve never really tried to fit neatly into any party box, and I don’t want to.”

The senator, who is serving her first term, stated in an article for the Arizona Republic that she ran for office with the promise “to be independent and work with anyone to achieve lasting results. I committed I would not demonize people I disagreed with, engage in name-calling, get distracted by political drama. I promised I would never bend to party pressure.”

After Democratic Sen. Raphael Warnock’s victory in Georgia’s runoff election on Tuesday, Democrats were expected to hold a 51-49 advantage in the Senate come January. With Vice President Kamala Harris casting the deciding Democratic vote in a tie, the Senate is now evenly split 50/50.

In an interview with Politico, Sinema stated that she will not caucus with Republicans and that she intends to continue voting the same way she has since being elected to the Senate in 2018 after serving three terms in the House. Nothing about my values or behavior will change, she declared.

“I don’t believe this is going to shake things up quite like everyone thinks,” Minnesota Sen. Amy Klobuchar told CNN, but she added, “It may change things with Arizona politics.” Klobuchar also stated that Sinema “tends not to go to the caucus meeting…except for rare moments where she’s advocating for something she cares about. That’s not going to change either.”

In a separate statement, White House Press Secretary Karine Jean-Pierre stated that 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.”

Sinema is up for reelection in 2024 and will almost certainly face a well-funded primary challenger after enraging much of the Democratic base by blocking or watering down progressive priorities like a minimum wage increase or President Biden’s large social spending initiatives. She has not stated whether she intends to run for re-election.

Rep. Ruben Gallego, who has a long history of feuding with Sinema, is the most prominent potential primary challenger.