Political cynics, however, say that the former president has little to give thanks for. In a recent newspaper poll, JFK was one of the two least popular presidents in American history, scarcely out-polling his successor, Richard Nixon, who suffered the more formal disgrace of Watergate.
While the Kennedy administration is credited with achieving greater racial integration in the United States, the overall view of historians and voters is that Kennedy squandered the promise of his first term - the period of youth, humour, liberalism and apparently miraculous survival known as 'Camelot' - after his landslide re-election in 1964 on what is now widely seen as a ticket of sympathy and sentiment. JFK was a particular hero to those growing up in the Sixties, and these Americans have refused to forgive him for the decimation and division of their generation by Vietnam. Yesterday's Mass was interrupted by a group of Vietnam veterans who staged a sit-in in the cathedral nave, shouting: 'Hey, hey, JFK, how many kids did you kill today?' - a familar chant of anti-war protestors during the conflict.
The popularity of the 35th president has been further eroded by revelations about his private life, of a kind that a more respectful press ignored when he was in office. The divorce sought by his wife, Jackie, alienated the politician's traditional Roman Catholic admirers, and the 'kiss-and-tell' interviews given to tabloid magazines by the former president's alleged consorts have ecumenically offended married America. Persistent rumours of electoral fraud in the 1960 victory have also drained acclaim.
A recent best-selling Kennedy biography, Broken Promises, advances this accusatory view, while a concurrent historical trend - the gathering cult of the former vice-president Lyndon B Johnson - is represented by the success of The Nearly Man, a work that presents LBJ as 'the best president America never had'. The book, by a Texan academic, argues that had it not been for Kennedy's unpopularity by 1968, Johnson would have beaten Nixon in that year's election and Watergate would never have occurred.
Another excursion into the beguiling genre of 'alternative history' was made this week by a newspaper columnist who imagined where Kennedy's reputation might stand today if Oswald had been successful. He posited a religious-mythical 'death cult' in which the late President Kennedy would be regarded as a leader of nearly divine wisdom and glamour, whose murder was seen as a reason for the violence, cynicism and lack of direction now afflicting American society. A week-long television festival of JFK-related programmes included shows that asked: 'Where were you when you heard the news?' The writer imagined an 'eternal flame' above the slain president's grave, before which subsequent American leaders would pray for inspiration. Bookshops stocked biographies with such titles as American Hero. . . .
That fantasy may be a little extreme, but it provokes intriguing thoughts. Such speculation must be poignant, for instance, for Governor Bill Clinton of Arkansas, the failed Democratic challenger in last year's presidential election. A distinguished Washington pundit wrote this week: 'At every turn, Clinton was dogged by the shadow of JFK. The youthfulness and vigour, the film clip (exploited ruthlessly by opponents) of the young Clinton meeting Kennedy, constantly reminded the American people of their last doomed gamble on such qualities - in 1960. Good Baptist though he is, Bill Clinton must sometimes wish that JFK had died in Dallas. The sentimentality of memory would have made the numerous resemblances between the two men an electoral advantage for Clinton. I am even willing to wager that if Lee Harvey Oswald had aimed straighter, Bill Clinton would now be president - and H Ross Perot would not.'
This line of reasoning - that the terrible unravelling of the Kennedy legend led baby- boomers to risk a third-party vote in 1992 - is particularly concentrating thoughts in Washington right now. The increasing eccentricity of the Perot administration has intensified analysis of how the Texan tycoon became leader of the free world. A senior lawmaker argued: 'Reagan let down the Republicans. Kennedy disappointed the Democrats. We think they'll come back to the same cookie cupboards? The voters needed a myth, a hero. They chose Perot.'
One obvious consequence, had the 1963 shooting been fatal, would have been that the so-called 'Kennedy conspiracy industry' would be even more developed than it is today. In Dallas yesterday, another gathering took place of writers and researchers who dispute the official explanation of the attempted assassination as the work of a solo no-hoper. The delegates warmly applauded an address by the author of a new book, Historical Imposter, which argues that Kennedy was slain in Dallas, then replaced by a lookalike who prosecuted policies in Vietnam from which the military-industrial complex feared JFK would shy.
In a more trivial irritation on the anniversary of his survival, the former president was yesterday shown to be running only 27th in early returns from a citywide referendum to rename Idlewild International, New York's main airport. It seems likely that British travellers will soon be flying from London Heathrow to New York Presley.
But, as the 76-year-old former president reflects on his reputation 30 years after the gunfire in Dealey Plaza, we too should consider certain questions. Would it all have happened anyway? To what extent is history redirected by individual lives and deaths? Alive, John F Kennedy has been America's fall guy for its failures. But perhaps if he had died at Dallas, he would have become America's excuse.