The political torch was handed over by the assassinated president's daughter Caroline, his brother Senator Teddy Kennedy, and nephew Patrick, with other grandchildren in the audience at American University. It was a moment of political symbolism that in time may be viewed as a pivotal moment in the 2008 race for the White House.

Ms Kennedy, 46, who rarely speaks in public, said her children, who were also present to support the Obama campaign, convinced her. He "offers that same sense of hope and inspiration" as her father did, she said. "Today isn't just about politics for me. It's personal," she went on. "I was too young to remember John Kennedy and I was just a child when Robert Kennedy ran for president. But in the stories I heard growing up, I saw how my grandparents and mother spoke about them, and about that period in our nation's life – a time of great hope and achievement."

Senator Kennedy called Mr Obama a "man with extraordinary gifts of leadership and character" and a worthy heir to his brother, and talked of America having another "rendezvous with destiny". The real value of Mr Kennedy's support will be in helping Mr Obama reach out to Hispanic voters in states such as California and New York where Hillary Clinton, his closest rival, has solid support. Mr Kennedy's reputation as a battler for social justice and civil rights may also convince rank-and-file Democrats who are union members to switch en masse to Mr Obama. He expects to hit the campaign trail before next Tuesday's elections, targeting Hispanic voters in Arizona, New Mexico and California.

It was on the same campus in 1963 that President Kennedy delivered a seminal speech calling for world peace and saying that a Pax Americana could never be achieved by force of arms.

The Kennedy endorsements had been sought desperately by Hillary Clinton. But her campaign tactics, which included questioning Mr Obama's record on issues such as the war in Iraq and Bill Clinton's intervention in South Carolina last week led to a blazing row between Senator Kennedy and Mr Clinton, culminating in a phone call on Sunday. Referring to Mr Clinton's much criticised remarks that Mr Obama's anti-Iraq war stance was a "fairy tale," Mr Kennedy boomed: "From the beginning, he opposed the war in Iraq. And let no one deny that truth."

To applause he said that "with Barack Obama, we will turn the page on the old politics of misrepresentation and distortion, with Barack Obama we will close the book on the old politics of race against race, gender against gender, ethnic group against ethnic group, and straight against gay."

Until yesterday, Mr Kennedy had remained neutral in the campaign, saying he was friends with Obama, Clinton and John Edwards. He barely mentioned his assassinated brothers, John and Robert Kennedy, and his endorsement of Mr Obama was unusually personal. "There was another time, when another young candidate was ... challenging America to cross a new frontier. He faced criticism from the preceding Democratic president, who was widely respected in the party," Mr Kennedy said, referring to Harry Truman. "And John Kennedy replied, 'The world is changing. The old ways will not do ... It is time for a new generation of leadership. So it is with Barack Obama."

In another important endorsement, Mr Obama picked up the support of Nobel Prize-winning author Toni Morrison, who cited his "creative imagination which coupled with brilliance equals wisdom".

Yesterday's political theatre overshadowed George Bush's final State of the Union address a few hours later. The President's fumbling attempts to achieve some relevance in the dying months of his presidency had an air of desperation.