Jean Kennedy Smith: 'Are We Doing the Best We Can for Everybody?'

Jan. 20, 2011— -- Jean Kennedy Smith, President John F. Kennedy's last remaining sibling, still has strong memories of the cold January day of her brother's inauguration 50 years ago.

"We had a big party at our house the night before," she told ABC News' Christiane Amanpour. "It was going to snow. It was in our garden in Georgetown. That was, sort of, the send-off and everybody was very up and excited."

Smith sat down with "Nightline" to mark the 50th anniversary of her brother's inauguration, and in a rare, exclusive interview she discussed how her brother's words still are relevant today.

Watch the full interview on "Nightline" tonight at 11:35 p.m. ET

"[What] we all remember is that very famous line about, 'Ask not what your country can do for you, ask what you can do for your country,'" Smith said. "And I think that sort of sums up his philosophy. That was a very strong sentiment that he believed deeply in."

The Kennedys are well known for their devotion to public service. Smith made her own contribution when she served as ambassador to Ireland under President Bill Clinton, helping to broker a historic peace agreement involving Northern Ireland.

In addition, no other family in public life has experienced as much tragic loss as the Kennedys. Smith is familiar with the kind of political violence waged on Rep. Gabrielle Giffords, D-Ariz., in Tucson, Ariz.

"It's happened, we all know, in the past," Smith said. "I don't think we should blame a whole group of people for it. I think, probably, it calls our attention to our country and, 'Are we doing the best we can for everybody?'"