From a Wall Street Journal story by Eliza Collins and Katy Stech Ferek headlined “Sen. Kyrsten Sinema Leaves Democratic Party to Become Independent”:

Centrist Sen. Kyrsten Sinema of Arizona said she was leaving the Democratic Party and would register as an independent, a move that complicates Democrats’ narrow control of the chamber.

“I have joined the growing numbers of Arizonans who reject party politics by declaring my independence from the broken partisan system in Washington,” she wrote in an opinion article in the Arizona Republic. “I registered as an Arizona independent.”