(NECN: Brian Burnell) - In Dallas' Dealey Plaza, the Texas Book Depository still stands, with the sixth floor window that was Lee Harvey Oswald's snipers perch, but that floor is now a museum.
Texans call Dealey Plaza a "vital crossroads for rail and road travel," and to worldwide visitors, it is the bend of the road where history took a violent turn. They, along with historians, can't help wondering how the world was changed by what happened there.
"It's very difficult still fully to assess the magnitude of the aftermath of his Presidency and the way it ended," Tufts Fletcher School of Law & Diplomacy Prof. Alan K. Henrikson says.
President John F. Kennedy was in Texas that November day to smooth over a Democratic party feud. Just three years in office, his style and youth defined him more than his domestic or foreign policy, which were both works in progress.
"He was very interested in arms control, particularly getting control of nuclear weapons," Henrikson says.
In November 1962, the national election was just one year away. The Cuban missile crisis, perhaps Kennedy's finest hour, was just a year old - and the Cold War was still on.
So on that November day, Kennedy planned to give conservative Texans a strong national security speech, touting the increase of tactical nuclear weapons, Polaris submarines, strategic bombers and the continued stationing of three to five million troops along what he called the communist frontier.
In 1963, that included Vietnam, where the U.S. already had 16,000 troops amid a growing conflict.
So what would JFK ultimately have done in Vietnam?
"He said about Vietnam, he said at one point, it's like taking a drink. You send more troops in, and you need to send more in," Henrikson says.
Kennedy might have shunned the hawkish proddings of his military joint chiefs. After all, he blamed them in part for the botched Cuban liberation at the Bay of Pigs. But few think he was ready to pull out of Vietnam in the face of hawkish political rival and likely election opponent Barry Goldwater.
"I think he probably would have stayed. But he probably would not have developed this into a a much, much larger-scaled war," Henrikson says.
But, with Kennedy gone, what did happen in history?
Lyndon B. Johnson, serving out Kennedy's term, was elected by a landslide. With legislative skills far stronger than JFK's, he was the southerner able to push through landmark civil rights legislation and wage a war on poverty.
But then Vietnam spoiled all of it for him.
"He didn't want to be the first American President -- Texas American President -- to lose a war," Henrikson says.
The war escalated, protests grew and a president fell.
Sixties idealism had glowed like that flame above President Kennedy's grave, but it burned the man who had fought poverty and racism in Kennedy's name.
The combination of the lingering Vietnam debacle and President Richard Nixon's Watergate lowered the voters' expectations of politicians - expectations that were boosted sky-high by Kennedy's high rhetoric about public service.
He'll always be recalled as president who used words powerfully, and never more so when speaking of our relations with Europe - and never more so than at the Berlin Wall.
"The Europeans really identified with because Kennedy had spent a lot of time in Europe, you know, when his father was ambassador to England. He traveled to Europe frequently when he was a member of the House of Representatives," University of Vermont's Garrison Nelson says.
"In a speech which he gave on the Fourth of July in Philadelphia in 1962, he issued what he called a Declaration of Inter-dependence," Henrikson says.
President Kennedy will forever be credited with a partial nuclear test ban treaty, the Peace Corps, and for the fulfilled pledge to put a man on the moon by the end of the 1960s - and for his words.
"We in this country, in this generation, are by destination, rather than choice, the watchmen on the walls of freedom."
A bold foreign policy vision of the 35th president of the United States from the speech he never got to deliver that fateful day in Dallas.