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The failure of the invasion of Cuba in April, 1961 by 1500 CIA-trained anti-Castro expatriates is generally attributed to President Kennedy's loss of nerve at the critical moment, when he cancelled the air strikes which were supposed to incapacitate Castro's air force. As a result, more than a hundred men were killed, the rest surrendered, and the Cuban exiles in America never forgave Kennedy for this "betrayal."
Insofar as anyone can know why history goes the way it does, this is plausible hypothesis, phrased that way, and especially stressing the lack of an uprising in support.
But it's important to note we don't know what would have happened if Kennedy *had* sent in air support. In retrospect, and especially considering how stable it has been since then, it doesn't seem especially likely that Castro's Cuba was ready for revolution in 1962 -- even if the invasion had been supported from the air. So had Kennedy sent in air support, it might have turned out even worse, with not just a CIA-sponsored invasion of expats (which could be and was disavowed) but actual armed aggression by United States forces against Cuban. Certainly an American pilot or two would have been captured. What then? Recall how costly was the Francis Gary Powers incident.
Cuba was a new and apparently promising Soviet client state, and Khruschev thought JFK was a fool and a naif -- what would have been the Soviet response to an actual attack on Cuba by American air forces? It doesn't seem very likely Khruschev would consider it an actual casus belli, not considering his own country's unreadiness for full-scale nulcear war, but would he have felt confident enough of his assessment of Kennedy to bluff one? If he did, would Kennedy have been able to figure out a resolution that involved neither the risk of nuclear war nor a humiliating climb-down of American power in the Caribbean? He was, after all, young, inexperienced, in physical pain, and yet wanting very much to appear cool and in command. A deadly combination.
The world may in fact be quite lucky that the Bay of Pigs failed the way it did, and Kennedy's decision to not support the invasion with air strikes may have been belated wisdom.