Sen. Dianne Feinstein, a veteran California Democrat, said Monday that she's running for another term.
The 84-year-old took to Twitter to declare that "I'm all in."
"I am running for re-election to the Senate. Lots more to do: ending gun violence, combating climate change, access to health care," Feinstein said.
She would be running for her fifth full term. She joined the Senate in 1992 after winning a special election. She had a serious challenge in 1994 from wealthy GOP Rep. Michael Huffington but has cruised since.
On Sunday, Feinstein told NBC's "Meet the Press" that "I'm ready for a good fight. I've got things to fight for."
Before coming to the Senate, Feinstein was a two-term mayor of San Francisco.
Feinstein is the top Democrat on the Judiciary Committee, where she has focused, often in futility, on gun control issues and immigration. She is also a senior member of the powerful Appropriations Committee, a post that has enabled her to tend to California's needs, and the intelligence panel.
She is an environmentalist but worked with House Majority Leader Kevin McCarthy, R-Calif., to broker an agreement on divisive Central Valley water issues that was opposed by former Democratic Sen. Barbara Boxer.
Feinstein, who had a pacemaker implanted in January, is the oldest senator in a chamber where it's not uncommon for people to serve into their 80s.
This story was updated.