I'm surprised to see you write this half-truth. It would not have been a crisis if only one of the two men had become involved. Actually Kennedy was lying to congress about his attempts to kill Castro and starve his country - the copper, sugar and oil embargoes, by the way, being what forced Cuba to ally with the USSR in the first place - so he had to present Russia's move to place nuclear missiles in Turkey as inexplicable bellicosity. This in spite of its approximate symmetry with Kennedy's decision to place nuclear warheads, obviously pointed at the Soviet Union, in Turkey and Italy the previous year. As a usually aggressive Republican quite clear-headedly put it at the time:
John J. McCloy wrote:even if the Soviet Union had missile bases in Cuba – which it hasn’t – why would we have any more right to invade Cuba than Khrushchev has to invade Turkey?
Kennedy was aware of the "ragged attack" lemma but glossed over it. I quote Gary Wills from his book
The Kennedy Imprisonment:
Gary Wills wrote:Would [Castro] launch his missiles in conjunction with a larger Russian attack again, knowing that he could incinerate his island as a side-blow in our response to Russia? Even if Castro had wanted to immolate his nation that way, his missiles would not have helped the Russians might, rather, have been a hindrance, because of the "ragged attack" problem. If missiles were launched simultaneously from Russia and Cuba, the Cuban ones, arriving first, would confirm the warning of Russian attack. Or, if Cuban missiles were to be launched later, radar warnings of the Russian ones firing would let us destroy the Cuban rockets in their silos.'
It's also generally accepted by historians that Kennedy felt embarrassed by his weak performance against Krushchev at the Vienna conference and was trying to save face by compensating (which also explains his later insistence on secrecy regarding the dismantling of the Turkish nuclear bases), and forgotten by the general public that Kennedy ran against Eisenhower from the Right on the point of relations with the Soviet Union. He went so far as to fabricate a mythical missile gap. Two years later, when the world was faced with its (to date) highest-stake Prisoners' Dilemma, Bertrand Russell sent a telegram to both Kennedy and Krushchev, telling them that they were acting insanely and ought to back down. Krushchev was receptive, while Kennedy was angered at Russell's arrogance.
As for Vietnam, it was Eisenhower who committed the first military advisers to Vietnam, as well as being the man who formulated the plan for the Bay of Pigs invasion. This is why I say there are methodological difficulties here. But against Eisenhower's 900 advisers we have Kennedy's 30,000, and Johnson's actual combatants.
Regarding policies and treaties that led to later conflicts, then, I think we must note that Clinton dismantled the weapons inspection regime in Iraq in the mid-90s before it was confirmed to have been completed, and that Kennedy stalled on any form of nuclear test-ban treaty just as he stalled civil rights and everything else. And I don't think it stands to Roosevelt's credit that he postponed the confrontation with Naziism, just as I don't think it stands to Wilson's credit that he led his country into an imperialist war against imperialism.