Sen. Dianne Feinstein announced Monday that she will run for re-election to the Senate. The California Democrat is the most senior female senator.

“I am running for reelection to the Senate,” Feinstein tweeted Monday. “Lots more to do: ending gun violence, combating climate change, access to healthcare. I’m all in!”

Inside Elections with Nathan L. Gonzales rates the race Solidly Democratic, but that doesn’t mean Feinstein won’t face a challenge.

Some California Democrats have been floated as potential primary challengers, including state Senate Democratic Leader Kevin de León. Entrepreneur Joseph N. Sanberg has also considered challenging Feinstein, according to Politico. And billionaire Tom Steyer would not rule out a Senate run, according to the Los Angeles Times. 

Feinstein already has the support of California’s junior senator. Kamala Harris, also a Democrat, issued a statement Monday saying she supported Feinstein and was thankful she was running for re-election.

“We are better off with her leadership and I look forward to continuing to fight together for California in the Senate,” Harris said in a Facebook post.

Feinstein won re-election in 2012 by 25 points. As of June 30, she had $3.6 million in cash on hand, according to Federal Election Commission documents. 

Feinstein, 84, was first elected to the Senate in 1992. In the 115th Congress she became the top Democrat on the Senate Judiciary Committee, which is one of the committees probing Russian interference in the 2016 election.

She is also a passionate supporter of gun control, and proposed her own legislation in the wake of last week’s shooting in Las Vegas, which left 59 dead and hundreds injured.

Feinstein discussed her proposal on NBC’s Meet the Press Sunday, and was asked whether she would run for re-election. The show’s moderator, Chuck Todd, pointed to a recent poll showing that half of Californians do not want her to run again.

“There are polls and then there are polls. I’m ready for a good fight,” Feinstein said. “I’ve got things to fight for. I’m in a position where I can be effective, and hopefully that means something to California.”

So far only one incumbent senator, Tennessee Republican Bob Corker, has announced his retirement. On average five senators have retired each cycle over the last 60 years.