CBS News Sunday Morning Anchor Charles Osgood talked with him on his farm in Pindar's Corner in upstate New York, in his office, an 1854 one-room schoolhouse, far from Washington.
At 73, Moynihan is a genuine intellectual: well-read, well-studied and well-published - 18 books and counting - on everything from the American family to ethnic politics to government secrecy.
"The great challenges of our time," says the senator, "have been challenges of ideas, the challenge of totalitarianism, Marxism."
"The remarkable thing about him in political terms is that he is and has remained an intellectual, and it's almost without precedent in American politics," says Steven Hess, an expert on Washington politics at the Brookings Institution and a long-time friend of Moynihan. "It's not just that he's got these ideas; he's got the power to do something about it, and he has the skill to dramatize it."
For decades Pat Moynihan and his ideas have helped shape and define the national debate on such issues as the deficit, the plight of poor children, and getting jobs for those on welfare. He has been a steadfast protector of Social Security, helping to save it from bankruptcy in the 1980s with Bob Dole, his friend and fellow senator. And from his first day in the Senate, he has been a key member of the Finance Committee.
But he says he will not miss the Senate. "No, 24 years is a long run," he says. "That's more than your share of time in office."
Was his retirement a difficult decision to make, or was it simply obvious to him that the time had come?
"There's simply a moment when, among other things, you look around, and your friends aren't there anymore," he says. "All the people you're with are certainly friendly. But they're not the ones you came into politics with, whose formative years were yours."
Moynihan was born in 1927 in Tulsa, Okla. But he grew up in New York City, the oldest of three children whose father had deserted them. He joined the Navy right out of high school, became a Fulbright scholar, and by age 34, was a member of John F. Kennedy's new frontier.
But it was what he wrote as assistant secretary of labor under President Johnson that earned him national repute. Ahead of his time, he wrote a report sounding the alarm on the growing trend of fatherlessness among poor, urban black families and the need to promote family stability.
But the report was not well received by many, and Moynihan was attacked for blaming the victim. By then, he had left Washington; he eventually taught at the Massachusetts Institute o Technology and Harvard University. But it wasn't long before a Republican president called him back.
Richard M. Nixon appointed him secretary of urban affairs.
Did Moynihan have any reservations about going to work for Nixon?
"No," says the senator. "He asked me at a time of tremendous urban travail - riots, troubles everywhere," he continues. "And he asked to come down and be adviser of urban affairs."
"And if you're not willing to do that, what kind of person are you?" he asks.
Hess, a Harvard colleague of Moynihan's, became his chief of staff. Hess recalls that his boss was "absolutely fascinated the president of the United States. It was a White House that was gray - Haldeman, Erlichman, and so forth - and then there was this flamboyant figure, and Nixon just loved it."
Moynihan moved on to become Nixon's U.S. ambassador to India and then ambassador to the United Nations under President Ford.
But what may be his greatest legacy is a project he began almost 40 years ago: renewing the nation's main street, Pennsylvania Avenue. It was completed just two years ago, with the opening of the Ronald Reagan Building.
"Clearly, there is something that is driving him - things he wants to say, things he wants to do," Hess observes.
And it has earned him the country's highest civilian award: the Presidential Medal of Freedom.
"It's something besides duty. It's patriotism. Pat Moynihan is a patriot," says Hess. "It's a very important thing, the degree to which he loves his country."
Today, if any one individual can share credit with Moynihan, it's his campaign manager and wife of 45 years, Elizabeth, many say.
"They have a very, very private life. You don't see them on the party scene in Washington," Hess says. "It helps to define him to know that his life is going back to his apartment and having dinner with his wife."
Moynihan says he feels he has answered the highest calling, and he has loved it.
"Think of all the progress that has been made," he marvels. "Here we are: world peace. We're the No. 1 power. The budget's in surplus. We have no unemployment to speak of, no inflation."
"These things were not thought possible," he continues. "Here they are. Don't take them for granted."