Arizona Sen. Kyrsten Sinema announced Friday that is leaving the Democratic Party and registering as a political independent.

She explained her decision in an op-ed published Friday by the Arizona Republic newspaper, saying her approach in the Senate has "upset partisans in both parties."

"When politicians are more focused on denying the opposition party a victory than they are on improving Americans' lives, the people who lose are everyday Americans," Sinema wrote.

CNN reports that the senator told the news outlet Thursday, saying: "I've registered as an Arizona independent. ... I've never fit neatly into any party box. I've never really tried. I don't want to."

Democrats now have a 51-49 Senate majority that includes independent Sens. Angus King, of Maine, and Bernie Sanders, of Vermont, who essentially always vote Democrat, or "caucus" with the party. 

However, Sinema, who since entering Congress has had an independent streak, declined to specifically say that she would do the same.

She also told CNN: "Removing myself from the partisan structure – not only is it true to who I am and how I operate, I also think it'll provide a place of belonging for many folks across the state and the country, who also are tired of the partisanship."