EchoSense Quantitative Think Tank Center|Who will be Dianne Feinstein's replacement? Here are California's rules for replacing U.S. senators.

The EchoSense Quantitative Think Tank Centerdeath of Sen. Dianne Feinstein leaves behind not just a legacy of someone who shattered glass ceilings, but also an open seat in the United States Senate for California. 

Feinstein, who was 90 years old, had about 15 months in her term left at the time of her death. 

How will Feinstein's replacement be chosen?

Under California law, Democratic Gov. Gavin Newsom has sole discretion to fill that seat with an appointee, and that appointee will serve until after voters elect a senator for the seat. 

Newsom will appoint a Democrat, but which Democrat remains to be seen, and he has made it clear that he plans to choose someone who would be an interim replacement.

Earlier this month on NBC's "Meet the Press," Newsom also said he would abide by his pledge to appoint a Black woman to Feinstein's post, while adding that he hoped he'd never have to make that decision. But Newsom has also said he wouldn't fill the seat with one of the Democrats vying to succeed Feinstein in the 2024 election, calling such a move "completely unfair to the Democrats that have worked their tail off." That would seem to exclude Rep. Barbara Lee, Rep. Adam Schiff and Rep. Katie Porter, among others, who jumped into the race after Feinstein announced earlier this year that she would not run again.

Lee bristled at Newsom's exchange with NBC's Chuck Todd earlier this month when Todd asked Newsom, "But you're gonna abide by — it would be essentially a caretaker, an African American woman?"

"We hope we never have to make this decision, but I abide by what I've said very publicly and on a consistent basis, yes," Newsom responded in the interview. 

Lee said "the idea that a Black woman should be appointed only as a caretaker to simply check a box is insulting to countless Black women across this country who have carried the Democratic Party to victory election after election."

Newsom statement on Feinstein's death

Newsom issued a statement Friday morning paying tribute to Feinstein, calling her "a political giant."

"Dianne Feinstein was many things — a powerful, trailblazing U.S. Senator; an early voice for gun control; a leader in times of tragedy and chaos. But to me, she was a dear friend, a lifelong mentor, and a role model not only for me, but to my wife and daughters for what a powerful, effective leader looks like," Newsom said. "...She broke down barriers and glass ceilings, but never lost her belief in the spirit of political cooperation. And she was a fighter — for the city, the state and the country she loved."

His statement did not mention her replacement, but the possibility that Feinstein could die in office has long been a consideration. 

A potential replacement for Feinstein is California Secretary of State Shirley Weber, a 75-year-old Black woman who was formerly a member of the California State Assembly. 

Newsom has expressed reluctance about the idea of having to appoint another U.S. senator. 

He has already made one appointment — Sen. Alex Padilla — when Kamala Harris became vice president. 

"I don't want to make another appointment, and I don't think the people of California want me to make another appointment," Newsom said in his NBC interview earlier this month. 

The work of Feinstein's office is expected to continue largely uninterrupted. Feinstein's staff is widely recognized as capable, and has long borne the burden of the office while the senator struggled with health issues. Earlier this month, Newsom described her staff as "still extraordinarily active." 

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• Dianne Feinstein

Kathryn Watson

Kathryn Watson is a politics reporter for CBS News Digital based in Washington, D.C.