ye110man- I don't think that you could put the other presidents at that time in the same category as Kennedy, when it came to charisma. I think that a lot of it had to do with television. He knew how to play to the cameras.
FDR and truman were up there. and macarthur. and they weren't americans but, churchill, ghandi, mandela, pope john xxiii, and the perons. hitler was very charismatic as well. and mao, stalin, castro, ho chi min, eisenhower, and de gaulle were, at the very least, all powerful leaders.
but i was thinking more about mlk jr and malcolm x.
that whole period between 1940 and 1965 is probably the most quoted era in history. i'm sure the TV had a lot to do with it but with such a disproportionate number of almost mythical leaders, i would think that world war ii and its aftermath created furtile grounds for those leaders to emerge.