US President Barack Obama has paid homage, alongside fellow two-term Democratic president Bill Clinton, at John F Kennedy's grave.
President Barack Obama has hailed the "daring" legacy and the "sober, square-jawed idealism" of John F Kennedy, as he marked the 50th anniversary of the 35th US president's assassination.
Obama also paid homage, alongside fellow two-term Democratic president Bill Clinton, at Kennedy's hillside grave to honour a man murdered at the age of just 46, but whose legend endures for Americans as a symbol of their nation's spirit and possibility.
Later, at a dinner honouring winners of the Presidential Medal of Freedom, an award minted by Kennedy, Obama said the wealthy slain president could have enjoyed a life of luxury and ease, but picked instead "a life in the arena."
"Fifty years later, John F Kennedy stands for posterity as he did in life, young, bold and daring," said Obama, who was two years old when the 35th US president was killed.
"He stays with us in our imagination, not because he left us so soon, but because he embodied the character of the people that he led," Obama added at the Smithsonian Institution's Museum of American History in Washington.
"In his idealism, his sober, square-jawed idealism, we are reminded that the power to change this country is ours."
Obama and Clinton, along with First Lady Michelle Obama and former secretary of state Hillary Clinton, earlier laid a large blue and white wreath on the sun-dappled grave of JFK, who was killed in Dallas on November 22, 1963.
They then stood together, with their hands on their hearts, as a bugler played the military lament "Taps."
Extended members of the Kennedy clan looked on at the tableau of presidential power, past, present and possibly future.
The observance came after Obama awarded Bill Clinton, and 15 other luminaries of the arts, sports, science and innovation the medal of freedom, his nation's highest civilian honour.
The Kennedy grave and eternal flame is at Arlington National Cemetery just outside Washington on a hillside with a paved area fashioned from Cape Cod granite quarried from near Kennedy's family homebase in Massachusetts.
The eternal flame was lit by Kennedy's wife Jacqueline Kennedy during his funeral in 1963 and she was buried beside her husband after her own death in 1994.
The poignant moment of remembrance came two days before the official half-century anniversary of the death of Kennedy, who was picked off as he rode an open-top limousine in Dallas, Texas, in a crime that traumatised the world.
The ceremonies have sparked a prolonged period of national and media reflection on the unfinished legacy of Kennedy, his tragedy-crossed family and the evocative period in the early 1960s when his political star illuminated the world.
Kennedy's closest living relative, his daughter Caroline, did not attend Wednesday's ceremony. An early supporter of Obama's presidential ambitions, she has just set off on a new chapter of her life as the US ambassador to Tokyo.
The joint Obama-Clinton appearance at the grave site represented the latest show of unity between two political power families who waged a bitter 2008 Democratic presidential nominating duel.
Hillary Clinton is now the red hot favourite to land the Democratic nomination for the 2016 election - but has not said whether she will make another run for the White House.
Presidents Clinton and Obama, two-term leaders both, laid claim to Kennedy's legacy in their own White House runs.
Clinton was famously pictured meeting Kennedy at an event in the White House Rose Garden in July 1963, and has reminisced about how he set eyes on the presidency himself after shaking JFK's hand.
Obama accepted Kennedy's torch of Democratic Party idealism in a key moment of the 2008 campaign when his late brother Senator Edward Kennedy endorsed the White House hopeful at American University in Washington.
The two presidents stood together at a painful political moment for Obama, when he may be looking for political inspiration, after being brought low by the botched implementation of his signature health care law.
Kennedy's killing was blamed on a gunman, Lee Harvey Oswald, who was said to be acting alone.
But the 50 years since have been replete with conspiracy theories centring on whether Oswald was the true culprit and if he was acting on his own initiative or was part of a wider plot.