On Friday, she said repeatedly that the identity of the president who would appoint her replacement did not figure in her retirement planning.

“There will be a president after this one, and I’m hopeful that that president will be a fine president,” she said.

Were Mr. Obama to name Justice Ginsburg’s successor, it would presumably be a one-for-one liberal swap that would not alter the court’s ideological balance. But if a Republican president is elected in 2016 and gets to name her successor, the court would be fundamentally reshaped.

Justice Ginsburg has survived two bouts with cancer, but her health is now good, she said, and her work ethic exceptional. There is no question, on the bench or in chambers, that she has full command of the complex legal issues that reach the court.

Her age has required only minor adjustments.

“I don’t water-ski anymore,” Justice Ginsburg said. “I haven’t gone horseback riding in four years. I haven’t ruled that out entirely. But water-skiing, those days are over.”