Kyrsten Sinema ditches Democrats to become an independent, undermining party's narrow Senate majority

• Arizona Sen. Kyrsten Sinema has announced that she is leaving the Democratic Party.

• Sinema confirmed on Friday that she has registered as an independent.

• Her move comes days after the Democrats won a narrow majority in the Senate.

Arizona Sen. Kyrsten Sinema has ditched the Democratic Party days after it won a narrow majority in the Senate.

In a tweet on Friday, Sinema announced that she has "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."

"Becoming an Independent won't change my work in the Senate; my service to Arizona remains the same," she wrote.

Her switch comes just days after the Democratic Party won a narrow majority in the Senate, after Georgia incumbent Sen. Raphael Warnock's won a run-off election in the state, beating out retired football player Herschel Walker.

Warnock's victory gave Democrats a razor-thin majority of 51-49 in the Senate, which has now been thrown into doubt.

Democrats can still rely on the tie-breaker vote of Vice President Kamala Harris, but the party had been looking forward to a period where they could afford to lose one senator's vote and still pass legislation.

Sinema told Politico that her closely held decision to leave the Democratic Pary reflects that she's "never really fit into a box of any political party"

In an op-ed for the Arizona Central, Sinema further explained her decision, saying that she is registering as an independent because of the national parties' "rigid partisanship", which she said had "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 wrote.

"In catering to the fringes, neither party has demonstrated much tolerance for diversity of thought," she added. "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."

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