Sen. Kyrsten Sinema leaving Democratic Party

WASHINGTON -- Arizona Sen. Kyrsten Sinema on Friday made a bombshell announcement that she is leaving the Democratic Party and will be registering as a political independent.

Democrats had held a 51-49 majority in the Senate following Raphael Warnock's victory over Herschel Walker in Georgia earlier this week. However, Sinema's move, while a blow to the Democrats, will be unlikely to change the power balance in the next Congress beginning in January as the Democrats' Senate majority already includes two independents: Bernie Sanders of Vermont and Angus King of Maine.

"Everyday Americans are increasingly left behind by national parties' rigid partisanship, which has hardened in recent years. Pressures in both parties pull leaders to the edges, allowing the loudest, most extreme voices to determine their respective parties' priorities and expecting the rest of us to fall in line," Sinema wrote in an op-ed for the Arizona Republic on Friday morning. "In catering to the fringes, neither party has demonstrated much tolerance for diversity of thought. Bipartisan compromise is seen as a rarely acceptable last resort, rather than the best way to achieve lasting progress. Payback against the opposition party has replaced thoughtful legislating."

ABC News Congressional Correspondent Rachel Scott reports she was told Sinema informed Senate Majority Leader Chuck Schumer Thursday night. Schumer had defended her as recently as Wednesday.

"Joe Manchin and Kyrsten Sinema are great members of our caucus. They are very valuable. They don't always agree with us on certain issues but they are tremendous contributors to our caucus, and we will continue to work with them," Schumer said.

She is up for reelection in Arizona in 2024.

In addition to her op-ed, Sinema released a statement Friday morning.

"When I ran for the U.S. Senate, I pledged to be independent and work with anyone to achieve lasting results. Over the past four years, I've worked proudly with other Senators in both parties and forged consensus on successful laws rebuilding our country's critical infrastructure, protecting our economic competitiveness, addressing historic drought to help secure our water future, expanding veterans' benefits, boosting innovation and small businesses, protecting marriage access for LGBTQ Americans, strengthening mental health care, and making our communities safer, more vibrant places in which to live and raise families," she said.

"In a natural extension of my service since I was first elected to Congress, I have joined the growing numbers of Arizonans who reject party politics by declaring my independence from the broken partisan system in Washington and formally registering as an Arizona Independent," she said.

The media rollout included an interview with CNN in which she said she intends to remain in her committee positions. "So when I come to work each day, it'll be the same, I'm going to still come to work and hopefully serve on the same committees I've been serving on and continue to work well with my colleagues of both political parties. And I'm not really spending much time worrying about what the mechanics look like for Washington, D.C.," she told CNN's Jake Tapper.

In a highly produced video released Friday morning, an opening slide introduces Sinema as an "Independent Voice for Arizona".

"We make decisions about what's best for ourselves and our families and communities. And so we don't spend a lot of time thinking about is this a Republican idea or is this a Democratic idea. Is this liberal or is this conservative? That's not how Arizonan's think. What we think about is what's right for my family, what's right for my community, what's right for my future," Sinema says in the video.

The video shows Sinema talking directly to camera in a purple dress, spliced with clips of Arizona landscape and footage of her town halls.

"Registering as an independent and showing up to work as an independence is a reflection of who I have always been and who Arizona is," Sinema says in the clip.

"I'm going to be the same person I've always been. That's who I am. I am going to show up to work I'm going to do my best for Arizona I'm going to continue to deliver results for everyday people. Nothing is going to change for me and I don't think anything is going to change for Arizona," she said.

ABC News' Oren Oppenheim contributed to this report.