The US is marking 50 years since President John F Kennedy was killed by an assassin's bullet in Dallas, Texas.
The city, which has long struggled with the legacy of the murder, hosts a series of official events on Friday.
Kennedy has been ranked among the nation's most revered presidents, though he served less than three years.
He is commemorated for his youthful vigour, his leadership through the Cuban missile crisis, and his challenge to America to put a man on the Moon.
But he is also remembered for ordering one of the most disastrous episodes of the Cold War, the failed Bay of Pigs invasion of communist Cuba by a CIA-trained paramilitary force of Cuban exiles.
Kennedy, a Democrat, was part of one of the most prominent US political dynasties of the 20th Century.
His father, Joseph, was a wealthy businessman who served in senior positions in the government of President Franklin Roosevelt, including as ambassador to Britain.
Two of his brothers later served as US senators and ran for president. One of them, Robert, was himself assassinated in 1968. Edward Kennedy, who died in 2009, was a champion of progressive causes including universal healthcare.
Among the official events in Dallas on Friday, the Dallas Symphony Orchestra will perform, Mayor Michael Rawlings will give an address, and bells will toll at the minute of Kennedy's death.
Those events and others conclude a week of tributes to the slain US leader.
On Wednesday, President Barack Obama laid a wreath at Kennedy's tomb at the national military cemetery in Arlington, Virginia. Mr Obama was joined by former President Bill Clinton, who as a youth met Kennedy.
Members of Kennedy's family stood by Mr Obama, Mr Clinton and former Secretary of State Hillary Clinton as a bugler played Taps, the traditional US military mourning song.
On 22 November 1963, Kennedy and his wife Jackie travelled to Dallas for early campaigning ahead of the following year's election.
Crowds of supporters lined the streets to catch a glimpse of the couple. As the presidential motorcade entered Dealey Plaza around 12:30 local time (18:30 GMT), Kennedy's convertible passed the Texas School Book Depository.
Gunshots rang out across the plaza. Bullets struck the president in the head and neck. Half and hour later, Kennedy was pronounced dead at a local hospital.
Soon after, Vice-President Lyndon Johnson was sworn in as president aboard Air Force One.
Lee Harvey Oswald, an employee at the depository, was arrested in connection with the shooting.
On 24 November 1963, he was scheduled to be transferred from police headquarters to a county jail when he was shot and killed by Jack Ruby, a local nightclub owner.
Although Kennedy's murder has provided endless fodder for conspiracy theorists, official inquiries have determined Oswald alone was responsible for the assassination.
The events of that November plunged the nation into mourning, and many Americans still recall where they were when they heard the news.
Texan Daniel Kendrick witnessed the shooting as a teenager at Dealey Plaza.
"I ran as fast as I could, I was afraid of getting hit. There were bullets coming down," he told the BBC.
Historian Robert Dallek said America had yet to recover from the assassination, in part because it was such a tremendous blow to the nation's self-esteem.
"The feeling is, this is not what we do in American politics," he told BBC North America Editor Mark Mardell. "This is not a banana republic. We don't have coups d'etat, we don't topple governments and kill our leaders."
Mr Dallek said Kennedy's popularity endured in part because Americans have been so disappointed in his successors.
"People want a better life in this country," he said. "They want to think their children are going to do better. And they associate this with Kennedy's youth, his promise, possibility."