84-year-old Democratic senator is bucking calls for her retirement and running for reelection
Feinstein announced the run on social media on Monday, noting her desire to keep fighting for various issues facing the country.
"I'm immensely proud of my service in the Senate and all I've done to help the people of California and the nation," Feinstein wrote on Facebook. "But there's still so much work left to do, from ending gun violence, to combating climate change, to ensuring proper and affordable access to healthcare, and to giving DREAMers the chance to stay in the United States."
Feinstein also announced the run on Twitter, using an unverified account that remained dormant since 2013. Feinstein's social media strategy created brief confusion on Twitter, until her spokesperson confirmed the validity of the account.
Feinstein has faced criticisms from the Democratic base as of late, fueling the possibility of a primary challenge in the coming months.
California State Senate President Pro Tempore Kevin de Leon, who is rumored to be a potential primary challenger, has been critical of Feinstein in recent weeks for her comments on President Donald Trump and suggestion that new gun laws could not have prevented the Las Vegas shooting.
Some worry that Feinstein might be too centrist for branches of the Democratic Party that want to move more to the left.
Michael Thaller, the chairman of the California Democratic Party's Progressive Caucus, told The San Jose Mercury News in June that there's a split "between the new breed and the old guard."
"It's not likely to heal if Dianne Feinstein runs for re-election," he said, adding, "it's time to get some new blood in there - some new, more progressive blood."
Sen. Kamala Harris, California's other senator, released a statement supporting Feinstein's reelection bid.
"What Californians get from Dianne is someone who sticks to her principles and achieves results regardless of powerful opponents, from the assaults weapons ban to the CIA torture report," Harris said. "We are better off with her leadership and I look forward to continuing to fight together for California in the Senate."