Trying to explain the political ambitions of Kennedy, who was sheltered from the glare of publicity after her father’s assassination in 1963 and has rarely emerged from it since, several people close to her said yesterday that she had long expressed a desire for a more active public life.

Joel I. Klein, chancellor of the New York City Department of Education and a Kennedy confidant, said he had a conversation with her eight years ago in which “it seemed to me she was now ready to start moving back into the public sector.” The Obama campaign, he said, “was obviously a major turning point,” adding that it “probably surprised” Kennedy how much she enjoyed the campaigning.

“Certainly this year she’s played a very significant role in the presidential campaign, and I think that has very much crystallized her interest in serving,” said John Shattuck, chief executive of the John F. Kennedy Presidential Library Foundation in Boston, who has worked with her since 2001. “But this is something that’s been a long time coming.”