Dianne Feinstein, the oldest member of the Senate, has died aged 90.
The California Democrat, the longest-serving female senator, had announced in February that she planned to retire at the end of her term. She had faced calls for her resignation over concerns about her health.
President Joe Biden described Ms Feinstein, who died on Thursday night after 30 years in the Senate, as “a pioneering American. A true trailblazer. And for Jill and me, a cherished friend.”
He said: “Serving in the Senate together for more than 15 years, I had a front row seat to what Dianne was able to accomplish... She’s made history in so many ways, and our country will benefit from her legacy for generations.
Mr Biden added: “Dianne was tough, sharp, always prepared, and never pulled a punch, but she was also a kind and loyal friend, and that’s what Jill and I will miss the most.
“As we mourn with her daughter Katherine and the Feinstein family, her team in the Senate, and the people of California, we take comfort that Dianne is reunited again with her beloved Richard. May God Bless Dianne Feinstein.”
Ms Feinstein was the first female president of the San Francisco Board of Supervisors and the first woman to become mayor of the city.
She suffered from a string of health issues after she was admitted to hospital for shingles in February, and was absent from the Senate for several months. She suffered multiple complications, including Ramsay Hunt syndrome and encephalitis.
The gun control advocate appeared confused at times, appearing unsure of how long she was absent and her diagnoses.
During a Senate Appropriations Committee hearing at the end of July, Ms Feinstein had to be prompted to vote “aye”.
Governor Gavin Newsom has the power to appoint a replacement to serve out the rest of Ms Feinstein’s term, keeping the Democratic majority in the chamber until January 2025.
Mr Newsom said in March 2021 he had a list of “multiple” replacements and he pledged to appoint a black woman if Ms Feinstein were to retire.
Issues could arise for the Democrats given the vacant chair on the Judiciary committee, where with her absence the party has lost its majority.
If Republicans object to her replacement being given a spot on the committee, it would leave Mr Biden unable to advance nominees – such as to the Supreme Court – without bipartisan support.
Earlier this year the Republican Party objected to Ms Feinstein being temporarily replaced on the committee while she was unwell, delaying the confirmation of several of Mr Biden’s appointments to federal judgeships and executive positions.