Editor's note: Tony Badger is the Paul Mellon Professor of American History at Cambridge University and Master of Clare College, Cambridge. He is the Chair of the Kennedy Memorial Trust.
(CNN) -- The John F. Kennedy who was elected in 1960 was not going to change the world. His major charge against the Eisenhower administration was that it was not prosecuting the Cold War vigorously.
He believed that its policy of Massive Retaliation in the event of any attack meant America would be incapable of a flexible response to a non-nuclear communist aggression in the Third World, where, he believed, the Cold War would be won or lost.
He aimed to close any missile gap (actually non-existent) with the Soviets. He aimed to beat the Russians to the moon. He planned to calm business fears by appointing a Republican Secretary of the Treasury.
He wanted to avoid coercive civil rights legislation or the use of federal troops to enforce segregation because he put his faith in white southern moderate leaders.
The John F. Kennedy who was assassinated in 1963 had begun to change the world. Admittedly, the failure of the Bay of Pigs invasion did not lessen the enthusiasm of either the president or his brother, Bobby, for covert action and counter-insurgency.
The military advisers committed to Vietnam were part of a flexible response -- but so was the inspirational Peace Corps.
But chastened by confronting the Russians over Berlin and missiles in Cuba, and reassured by the knowledge that the missile build-up had guaranteed a measure of Cold War stability, Kennedy moved to lessen Cold War tensions and the dangers of nuclear war.
He started a backchannel correspondence with Khrushchev. He negotiated, in the face of military opposition, a Test Ban Treaty which aimed to eliminate nuclear tests in the atmosphere. He was the first American president in the Cold War to talk about the Soviet Union as an adversary with whom the United States should peacefully compete, rather than an enemy to be defeated militarily.
Except in the Yom Kippur war in 1973 the world never again came close to a nuclear holocaust. Under JFK the first steps to détente were taken. Kennedy was the first president to understand the Sino-Soviet split.
At home, he proposed a tax cut, not as a result of a budget surplus, but despite a budget deficit, in order to stimulate the economy. As a result of the crisis created by violent resistance in the South to civil rights protest, the president was forced to do the two things he did not want to do.
He sent in federal troops to force the admission of a black student to the University of Mississippi. After the Birmingham demonstrations and the defiance of Governor Wallace on the steps of the University of Alabama, he went on national television to promise strong civil rights legislation and acknowledged for the first time that civil rights was an inescapable moral issue.
Kennedy's assassination and Johnson's masterly leadership guaranteed the eventual passage of the civil rights bill and the tax cut. It did not interrupt the progress towards détente.
But Kennedy's death did put an end to third-party efforts to normalize relations with Cuba. Kennedy might have gone on to re-orient policy towards China. Would he have avoided the Vietnam disaster?
Kennedy's defenders argue passionately that, protected by a big re-election win in 1964, he would have withdrawn American troops from Vietnam. But his Vietnam policy in late 1963 in which he acquiesced in the overthrow of President Diem's government was already locked in a policy of sustaining a South Vietnam government that was ready to fight the communists.
He had effectively narrowed the options available to his successor. There is little evidence that he would have sanctioned the "loss" of South Vietnam.
Faced with the impossibility of finding a government that was both popular and willing to fight the Vietcong, how would Kennedy have avoided the commitment of ground troops in 1965?
Advised by McGeorge Bundy and Robert McNamara, who guided Vietnam policy under both JFK and LBJ, would Kennedy have been prepared to scale down the American commitment and see the South Vietnam regime collapse?
British Ambassador and friend of the Kennedys, David Ormsby-Gore, tried to console Jackie Kennedy by telling her that the late president, "had great things to do and would have done them."
The jury may be out on that judgment. But the British reacted with the same grief as the Americans to a lifer cut short, to the cruel death of a young man whose vigor and youth contrasted so markedly with the contemporary political leaders of an older generation: De Gaulle, Adenauer and Macmillan.
They established at Runnymede, the site of the signing of Magna Carta, a memorial funded by popular appeal and driven by cross-party consensus on an acre of land permanently ceded to the United States.
David Ormsby-Gore, as Lord Harlech, was the first chair of the Kennedy Memorial Trust which also awarded scholarships to the "best and the brightest" of British students to do graduate work at Harvard and MIT.
On Friday, as current chair of the Trust, I will be laying a wreath at the memorial. Why does JFK's memory still resonate? Perhaps it is because contemporary American politics is dysfunctional and anti-intellectual fundamentalism is so rampant in American public life.
Kennedy was familiar enough with congressional gridlock and only too aware of the paranoid style of American politics on the extreme right. But he was the modern American president who was most comfortable in his own skin, who surrounded himself with intellectuals and delighted in their company, and who made government service an honorable calling after the ravages of McCarthyism.
Kennedy may not have changed the world and his assassination may not have significantly altered America's future, but 50 years on it is not surprising that his memory still evokes a profound sense of loss.
The opinions in this commentary are solely those of Tony Badger.