Chief Justice John G. Roberts Jr. wrote the majority opinion, and he quoted extensively from a 2009 decision that had, temporarily as it turned out, let the heart of the Voting Rights Act survive. Eight members of the court, including Justice Ginsburg, had signed the earlier decision.

On Friday, she said she did not regret her earlier vote, as the result in the 2009 case was correct. But she said she should have distanced herself from the majority opinion’s language. “If you think it’s going to do real damage, you don’t sign on to it,” she said. “I was mistaken in that case.”

Some commentators have said that the two voting rights decisions are an example of the long game Chief Justice Roberts seems to be playing in several areas of the law, including campaign finance and affirmative action. Justice Ginsburg’s lone dissent in June’s affirmative action case, leaving in place the University of Texas’ admissions plan but requiring lower courts to judge it against a more demanding standard, may suggest that she is alert to the chief justice’s apparent strategy.

Justice Ginsburg is by her own description “this little tiny little woman,” and she speaks in a murmur inflected with a Brooklyn accent. But she is a formidable force on the bench, often asking the first question at oral arguments in a way that frames the discussion that follows.

She has always been “a night person,” she said, but she has worked even later into the small hours since her husband, Martin D. Ginsburg, a tax lawyer, chef and wit, died in 2010. Since then, she said, there is no one to call her to bed and turn out the lights.

She works out twice a week with a trainer and said her doctors at the National Institutes of Health say she is in fine health.

“Ever since my colorectal cancer in 1999, I have been followed by the N.I.H.,” she said. “That was very lucky for me because they detected my pancreatic cancer at a very early stage” in 2009.