Sen. Dianne Feinstein had to be corrected and told to vote during a Senate Appropriations Committee hearing on Thursday.
The California Democrat, who has been in frail health following a shingles diagnosis in the spring, has appeared confused at times since her return to the Capitol.
Feinstein, who at 90 is the oldest member serving in the US Senate, has faced questions about her health in recent years, and members of her own party called on her to resign her Senate seat after an extended absence earlier this year following the shingles diagnosis. She returned to Washington in June.
During Thursday's hearing, Feinstein was meant to cast her vote on the Defense Appropriations bill, requiring her to say "Aye" or "Nay," when her name was called. When she didn't answer, Democratic Sen. Patty Murray of Washington state tried to prompt her.
"Say aye," she said, repeating herself three times to Feinstein.
Feinstein then started to read from prepared remarks, and was interrupted by an aide whispering in her ear.
"Yeah," Murray said once again. "Just say 'aye.'"
"OK, just," Feinstein replied.
"Aye," Murray repeated once more.
Then Feinstein sat back in her chair. "Aye," she said, casting her vote.
Feinstein announced earlier this year that she will not run for reelection in 2024. During her absence this spring, Democrats publicly worried her absence would slow the process of confirming nominees through the Senate Judiciary Committee, where Feinstein is a member. At the time, Feinstein disputed that characterization, saying that judicial nominations had not been significantly delayed.
The capabilities of some of the Senate's oldest members has been in sharp focus in Washington this week, following a moment Wednesday afternoon when Senate Minority Leader Mitch McConnell appeared to freeze up in the middle of a news conference and was escorted away from reporters. McConnell, who is 81 and the chamber's fourth oldest member, returned minutes later, saying he was "fine." An aide later told CNN the Kentucky Republican had felt light-headed.