Feinstein, 88, said that the record shows she is an effective politician.
"I remain committed to do what I said I would when I was re-elected in 2018: fight for Californians, especially on the economy and the key issues for California of water and fire," she said in a statement issued by her office. “While I have focused for much of the past year on my husband’s health and ultimate passing, I have remained committed to achieving results and I’d put my record up against anyone’s."
Feinstein said that, in the last few months, she has led the reauthorization of the Violence Against Women Act and secured additional funding to retain federal firefighters to help California prepare for the upcoming wildfire season.
“The real question is whether I’m still an effective representative for 40 million Californians, and the record shows that I am," she said.
A report by The San Francisco Chronicle cited four anonymous senators — including three Democrats — and three former Feinstein staffers as well as a Democratic lawmaker from California who said her memory is rapidly deteriorating and it appears she can no longer fulfill her responsibilities in Congress without her staff doing a good deal of the work. They also said her memory lapses did not appear to be constant.
The story quoted one anonymous Democratic senator who said Feinstein has a hard time keeping up with conversations. Another lawmaker, identified only as a California Democrat, told the newspaper that they had to reintroduce themselves to Feinstein several times during an interaction that spanned several hours.
NBC News has not independently verified the Chronicle's reporting.
Feinstein, who originally declined to be interviewed for the article, spoke with the newspaper's editorial board by phone after it was published Thursday.
"I meet regularly with leaders,” Feinstein told the board. "I’m not isolated. I see people. My attendance is good. I put in the hours. We represent a huge state. And so I’m rather puzzled by all of this."
She said no one has directly addressed these issues with her: "No, that conversation has not happened."
Feinstein, a member of the Judiciary Committee, participated in all rounds of the televised Supreme Court confirmation hearings for Judge Ketanji Brown Jackson, who was confirmed by a 53-47 vote in the Senate.
Feinstein, who has served in the Senate since 1992 and is the oldest member of Congress, is not up for re-election until 2024.
Her husband, Richard Blum, died at the age of 86 in February after having cancer.