Washington — Democratic Sen. Kyrsten Sinema of Arizona announced Friday that she's registered as an independent but doesn't plan to caucus with Republicans, ensuring Democrats will retain their narrow majority in the Senate. Sinema, who has modeled her political approach on the renegade style of the late Sen. John McCain, R-Ariz., and has frustrated Democratic colleagues at times with her overtures to Republicans and opposition to Democratic priorities, said she was "declaring my independence from the broken partisan system in Washington." "I know some people might be a little bit surprised by this, but actually, I think it makes a lot of sense," Sinema told CNN on Thursday. "I've never fit neatly into any party box. I've never really tried. I don't want to." A Democratic aide told CBS News Sinema told Senate Majority Leader Chuck Schumer, D-N.Y., of her decision Thursday. The first-term senator wrote in the Arizona Republic that she came into office pledging "to be independent and wor