East Bay Rep. Barbara Lee on Tuesday formally entered the race to succeed Dianne Feinstein in the U.S. Senate, shaking up a field of Democratic contenders vying for the powerful seat the retiring incumbent has held for 30 years.

The two other Democratic contestants, Reps. Katie Porter of Irvine and Adam Schiff of Los Angeles, are rising stars in the party. But Lee — the first candidate from Northern California and the highest-ranking Black woman appointed to House Democratic leadership — has built up a solid resume as a progressive voice in Congress over her quarter century in Congress.

“She’s deeply respected in California politics,” said UC San Diego political science professor Thad Kousser. “Her progressive credentials can’t be challenged.”

Lee’s announcement Tuesday wasn’t a surprise. She’d already signaled her intent to run when Feinstein announced last week she wouldn’t seek another term in 2024 and submitted paperwork Friday to that effect. At the time, Lee said she’d offer more this week.

In a video posted Tuesday on Twitter, Lee ran through a list of the personal and professional battles she has taken on in her life, including fighting to be her school’s first Black cheerleader, championing protections for survivors of domestic violence and being the only member of Congress to vote against the authorization for the use of military force after the Sept. 11, 2001, terrorist attacks.

In 2021, she was one of several Congress members who shared stories about their own abortions during a congressional hearing — in her case, at a back-alley clinic in Mexico before California legalized the procedure in the 1960s.

“I’ve never backed down from doing what’s right. And I never will,” Lee said in the video. “Californians deserve a strong, progressive leader who has delivered real change.”

Feinstein, the former San Francisco mayor elected to the Senate in 1992, has been a leading voice in Congress for stricter gun laws, environmental protection and gay rights. But she has a centrist streak that has irritated the Democrats’ younger, more strident and increasingly influential progressive wing.

Feinstein drew barbs from the left over her reluctance to eliminate filibuster rules that require a large Senate majority to move legislative bills and for praising and hugging Republican Sen. Lindsey Graham after the Senate confirmed former President Donald Trump’s nominee, Amy Coney Barrett, to the U.S Supreme Court.

In recent years, Feinstein has endured leaks to the press suggesting that, at 89 and the Senate’s oldest member, she’s mentally slipping and should bow out.

Porter, a 49-year-old consumer lawyer, gained admiration for her tough questioning of bank executives and use of a whiteboard to emphasize points she wanted to make during congressional hearings. Schiff, 62, became a household name as he served as the lead prosecutor in Trump’s first impeachment trial. Both have been leaders in the Congressional Progressive Caucus and announced their Senate bids last month before Feinstein said she’d retire.

The three Democratic candidates occupy much of the same political terrain, so the race could be shaped by other distinguishing factors.

Lee’s district includes Oakland and Berkeley and is one of the most liberal in the country. Porter represents a politically divided district in Orange County that was once a conservative stronghold. Schiff’s district includes Hollywood and Burbank, where he lives.

Kousser said Lee’s entry is likely to discourage other Democrats, such as Bay Area Rep. Ro Khanna, a Bernie Sanders ally, from joining the fray, and that it probably helps Schiff more than Porter, who’s seen as more to his left. Schiff once belonged to the House’s centrist Blue Dog Coalition, and Feinstein’s decisive 2018 defeat of fellow Democrat Kevin de León — a challenge from her left — signaled the state’s voters aren’t necessarily looking for a more liberal alternative.

“If Dianne Feinstein stayed in this race, she’d still be tough to beat,” Kousser said, adding that Schiff “hopes he’ll inherit Dianne Feinstein’s voters, as well as those who want a new generation of leaders.”

For voters in California’s open primary, where the top contenders advance to the November election regardless of party affiliation, style, demographics and personal appeal may be bigger factors, given there’s little daylight between Democratic hopefuls on issues.

Schiff and Porter are White, and there are no Black women now in the Senate, where only two — Vice President Kamala Harris and Carol Moseley Braun of Illinois — have previously served. Lee is the highest-ranking Black woman appointed to House Democratic leadership, serving as co-chair of the Policy and Steering Committee.

Though 13 years younger than Feinstein, Lee at 76 is the oldest of the candidates and made a point Tuesday of addressing any concerns about her age.

“For those who say my time has passed, well, when does making change go out of style?” she said in the video. “I don’t quit. I don’t give up.”

Democrats are expected to dominate the contest in deep-blue California, where a Republican hasn’t won a statewide race since 2006. Only Democrats made the state’s November ballots for U.S. Senate in 2016 and 2018.

Still, a crowded Democratic field opens a door for a Republican or independent. In last year’s primary, Republican lawyer Mark Meuser made the runoff against Democrat Alex Padilla, who was appointed by Gov. Gavin Newsom to fill Harris’ vacated seat. Padilla handily beat Meuser in November, but it suggests the right Republican or independent could make it a contest.

Policy differences between the three Democrats are “so slight it allows room for a Republican to get into the race,” said Harmeet Dhillon, a San Francisco lawyer and National Committeewoman of the Republican National Committee for California.

Kousser didn’t disagree.

“I still think the right Republican with the required resources could succeed in California,” he said.

But it would take tens of millions of dollars — probably from independent wealth — to win, Dhillon added.

“We might get Republican in the top two,” Dhillon said, “but in terms of winning, I think that’s challenging at this time.”

Associated Press writer Michael R. Blood contributed to this report.