Bass, a fellow Democrat who served in Congress with Lee for over a decade, endorsed her former colleague and friend in the contest to replace Sen. Dianne Feinstein, also a Democrat, who announced in February that she would retire when her current term ends in January 2025.

The mayor said Lee’s experience as a “progressive fighter” in Washington is what the state needs.

“I’ve seen her leadership firsthand,” Bass tweeted. “Her work in a divided government to secure billions of dollars in COVID relief for underserved communities is just one example of the type of principled and tenacious leadership she will bring” as the state’s next U.S. senator.

Bass’ endorsement in what is expected to be a hotly contested race was being watched closely following her victory in last year’s mayoral race, which elevated her to national prominence as the first woman to lead California’s largest city.

In 2020, Bass joined activists and other politicians in urging Gov. Gavin Newsom to appoint a Black woman to replace Kamala Harris, who vacated her seat representing California in the Senate after her election as vice president.

In an interview at the time with L.A.’s Fox 11 affiliate, Bass noted that without Harris, the Senate would have “one African American Democrat, one African American Republican, no African American women.”

“I do believe that there should be an African American woman in the Congress,” she said. “I feel bad for the governor. He’s in a heck of a spot. It’s a tough decision to make.”

Newsom instead selected then-Secretary of State Alex Padilla to fill the post, making him the first Latino to represent California in the Senate, but the governor promised to appoint a Black woman if another Senate vacancy opened up.

Feinstein’s plan to remain in office through the end of her term, however, puts the decision on her successor in the hands of California voters instead of the governor.

When Bass later ran for mayor, Harris and her husband, Doug Emhoff, were a regular presence on the campaign trail. After Bass won, Harris swore the former congresswoman in as the city’s first female mayor and second Black mayor.

Former House Speaker Nancy Pelosi — who is close to Bass — endorsed Rep. Adam B. Schiff (D-Burbank) in the Senate race in February. Schiff endorsed Bass for mayor last year and campaigned by her side in the final days before November’s election.

Lee, of Oakland, trailed Schiff and their fellow House Democrat, Rep. Katie Porter of Irvine, in a recent UC Berkeley Institute of Governmental Studies poll on the Senate race. The survey, co-sponsored by The Times, was conducted after Lee indicated she would run but before she officially announced her bid.

Schiff had the support of 22% of the registered voters surveyed, compared with 20% who backed Porter and 6% who supported Lee. A majority of voters said they hadn’t made up their minds on a candidate, so the race still has plenty of room to shift before the March 2024 primary.

Lee said she was grateful for Bass’ support and excited to work with her to help people living on the edge.

“Mayor Bass’s work to serve Californians — as an Assemblywoman and Congresswoman, and now as Mayor — and to break monumental barriers while doing so, has been an inspiration to me and so many others,” Lee said. “I’m honored to have her support of my campaign.”

Lee stopped by Los Angeles City Hall last Thursday for the ceremonial swearing-in of new State Controller Malia Cohen. Standing in the rotunda lobby, she was asked about the prospects of her candidacy.

“I just launched my campaign two days ago,” she said, adding that she felt “fine” about the race.

While she has long represented part of the Bay Area, Lee noted she’s a San Fernando High School alumna, and said she’d be campaigning across the state over the next year: “I’m going for votes everywhere.”