WASHINGTON — Senator Dianne Feinstein, Democrat of California, announced on Tuesday that she would not seek re-election in 2024 but would finish out her term in Congress, making official a retirement that was long assumed by her colleagues, who had grown concerned about her memory issues.
The move clears the way for what is expected to be a costly and competitive race for the seat she has held for three decades.
Ms. Feinstein, 89, a trailblazing Democratic power broker, has had acute short-term memory issues for years that have raised concerns among those who interact with her. Even as she has faced questions about her ability to represent the 40 million residents of California, Ms. Feinstein has refused to publicly acknowledge the problems.
She said in a statement that she planned to “accomplish as much for California as I can through the end of next year, when my term ends,” meaning Gov. Gavin Newsom of California would not appoint a replacement to fill her seat.
Speaking to reporters, Ms. Feinstein joked that she was not leaving Congress until the end of next year, “so don’t hold your breath.” She explained her decision by saying that “there are times for all things under the sun, and I think that will be the right time.”
The announcement was greeted with some poignancy and some relief by some of her colleagues and people close to her.
“She’s a legend, a legend in California as the first woman senator,” said Senator Chuck Schumer, Democrat of New York and the majority leader. He said he had never seen such a long standing ovation at a caucus lunch as Ms. Feinstein received on Tuesday when she informed her colleagues of her decision. She gave a “heartwarming and tearful address,” he added.
President Biden praised Ms. Feinstein for leading efforts to reduce gun violence and protect the environment. “I’ve served with more U.S. senators than just about anyone,” he said in a statement. “I can honestly say that Dianne Feinstein is one of the very best. I look forward to continuing to work with her as she serves out her term.”
Since her husband, the financier and Democratic megadonor Richard C. Blum, died a year ago, Ms. Feinstein has been under immense strain, people close to her said. After his death, some tried to broach the subject of whether she might step away from the Senate, but she was set on continuing to work.
At the Senate Democratic Caucus lunch on Tuesday, Ms. Feinstein talked to her colleagues about “what she’s been through the past few years,” said Senator Amy Klobuchar, Democrat of Minnesota.
Ms. Feinstein’s stepdaughter, Annette Blum, said in an interview on Tuesday that she was “very proud of her long and impactful career” and that the family agreed that “this is the time for her to pass the torch.”
Some California Democrats did not wait for Ms. Feinstein to announce her plans to start campaigning for her seat. Representative Katie Porter, who flipped a previously Republican district in Orange County in 2018 and has earned Democratic accolades for her sharp questioning of corporate executives in congressional hearings, was the first to announce her campaign last month. Representative Adam B. Schiff, a former leader of the House Intelligence Committee and the manager of President Donald J. Trump’s first impeachment trial, entered the race a couple of weeks later.
Representative Barbara Lee, a progressive stalwart from the Bay Area, is expected to announce her candidacy by the end of the month. Representative Ro Khanna is seen as another possible candidate.
The Republican field is less clear. In California, all candidates run on the same primary ballot regardless of party, and the top two advance to the general election, so two Democrats could potentially face each other in November 2024.
Ms. Feinstein said Tuesday she would hold off on issuing any endorsement in the race, at least for a few months.
Over a half-century career in politics, Ms. Feinstein rose from a member of the San Francisco board of supervisors to the heights of Democratic power. As a senator, she helped create Joshua Tree National Park in Southern California, wrote the 1994 assault weapons ban and, as the detail-oriented, hard-charging chairwoman of the Intelligence Committee, produced the 6,700-page torture report on the excesses of the war on terrorism.
In recent years, however, Ms. Feinstein has been more sidelined. In 2020, amid questions about her ability to lead the powerful Judiciary Committee, she was forced out as the top Democrat on the panel. She was deeply disappointed by the move, according to people close to her, who said she was fully competent to lead the panel and had dutifully waited her turn.
Ms. Feinstein these days struggles to recall the names of colleagues, frequently has little recollection of meetings or telephone conversations, and at times walks around in a state of befuddlement — including about why she has been dogged by questions about whether she was fit to serve in the Senate.
“She has impressed me at every turn,” said Senator Chris Coons, Democrat of Delaware. He said that over the years, “her dignified, forceful style of leadership on the Judiciary Committee, where I served with her, and on the Intelligence Committee showed how much impact a senator can have.”
“She will be deeply missed,” he said.
Maggie Astor, Catie Edmondson and Carl Hulse contributed reporting.