Chantal Da Silva is a breaking news editor for NBC News Digital based in London.
Mike Memoli is an NBC News correspondent.
Arizona Sen. Kyrsten Sinema has announced she is leaving the Democratic Party and officially registering as an independent.
"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," Sinema, 46, tweeted early Friday morning.
"Over the past four years, I’ve worked proudly with other Senators in both parties and forged consensus on successful laws helping everyday Arizonans build better lives for themselves and their families," the Arizona senator said. "Becoming an Independent won’t change my work in the Senate; my service to Arizona remains the same."
Sinema's announcement came days after Democrats reached a 51-49 majority in the upper chamber following Sen. Raphael Warnock’s victory in Georgia.
The Biden administration was informed of Sinema’s decision to leave the Democratic Party “mid-afternoon” on Thursday, a senior administration official said.
The official added that the White House has been told she will continue to caucus with the Democrats, becoming a third independent to do so, along with Sen. Bernie Sanders of Vermont and Angus King of Maine.
“[We] don’t really think it changes much except her re-election path,” the official said.
In an op-ed published by The Arizona Republic newspaper, Sinema expanded on her decision, saying that everday Americans were being "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," she said, adding: "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.".
Notably, Sinema did not join the rest of the Arizona Democratic delegation on Air Force One earlier this week as President Biden held his first event in the state as president.
Biden did acknowledge Sinema in his remarks, however, saying: “I want to thank Senator Sinema, who can’t be with us today. She’s in Washington working on another major piece of legislation. A tremendous advocate for the people of Arizona and a leader in so many issues important to this state."