Senator Dianne Feinstein is returning to Washington after months of absence led to calls from within her own party to resign.
The 89-year-old California Democrat was briefly hospitalised after being diagnosed with shingles in late February and was recovering at home.
Critics claimed her absence complicated efforts by Democrats in the Senate to nominate federal judges.
Ms Feinstein denied last week there had been a slowdown.
Her office confirmed to the BBC on Tuesday that she was travelling from California to Washington DC.
The San Francisco Chronicle first reported the news of Ms Feinstein’s return.
Ms Feinstein is the oldest US senator and has faced questions in recent years about her health. Her office has long maintained that she is able to carry out her duties. Ms Feinstein has already said she will not seek re-election in 2024.
But her fitness came once again under scrutiny after she was diagnosed with the shingles virus in February. The illness, which causes painful rashes, can be serious for seniors.
After a brief time in hospital, Ms Feinstein continued to recover and work at home in San Francisco.
Her absence caused headaches for Senate Democrats back in Washington, who hold a narrow one-seat majority in the US Senate and on the powerful Senate Judiciary Committee, where Ms Feinstein serves.
Democrats have worried that Ms Feinstein’s absence from the judiciary committee would complicate their ability to confirm federal judges, one of the few priorities they can accomplish with a divided Congress.
The party is eager to install liberal-leaning justices to the lifetime posts after Republicans spent years remaking the federal judiciary under former President Donald Trump.
Ms Feinstein has maintained her inability to vote did not hamper her party’s ability to confirm federal judges.
“The Senate continues to swiftly confirm highly qualified individuals to the federal judiciary, including seven more judicial nominees who were confirmed this week,” she said in a 4 May statement.
“There has been no slowdown.”
Progressive Democrats began calling for her to resign in mid-April after Republicans refused Ms Feinstein’s request to temporarily replace her on the judiciary committee and Senate Majority Leader Chuck Schumer declined to provide a timeline for her return.
Reps Ro Khanna, Alexandria Ocasio-Cortez, and Rashida Tlaib, all Democrats, have called on Ms Feinstein to step down before her term ends so Democrats could pass their legislative priorities.
While Ms Feinstein has faced calls to resign before, this latest round of demands “does feel different, because she’s missing these votes and the Senate is so closely divided,” Eric Schickler, co-director of the Institute of Governmental Studies at the University of California, Berkeley, told the BBC last month.
A high-profile race to replace Ms Feinstein is already underway in California. Representatives Adam Schiff, Barbara Lee, and Katie Porter are all vying for the a once-in-a-lifetime seat.
Should Ms Feinstein not finish her term for any reason, California Governor Gavin Newsom would appoint her replacement.
Ms Feinstein, however, has given no indication she plans to step down early.
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