POD: Kennedy is wounded but not killed by Oswald, and lives to win a second term. Civil rights legislation and anti-poverty programs as Johnson OTL, but perhaps a bit slower and more tentative: similar problems with riots etc. as OTL.
Major difference is in Vietnam, where Kennedy is more reluctant to commit large numbers of troops, and perfers to stick with a beefed-up Special Forces mission, training, advisors, etc. US involvement is less noticeable and for a while remains a secondary issue in US politics. There is still a Counterculture, but Vietnam is not really on the program for political action, compared to civil rights, opressive social structures, racism, sexism, squareness, etc.
Unfortunately, the Special Forces prove to be insufficient, the situation in South Vietnam rapidly gets worse, and to prevent a total collapse, Kennedy has to carry out a massive injection of US forces into South Vietnam in his last year in office. Nixon is able to convince people that Kennedy's handling of the Vietnamese situation has been hamhanded, and running on a promise that he can salvage the mess and bring victory (at this point popular opinion still sees this as an analogy to the Korean war rather than a quagmire in the making) and on "law and order" (the anti-war left haven't yet made themselves a source of paranoia, but the Counterculture is still very annoying, and the black population haven't reacted well to Kennedy's sluggishness on civil rights) manages to pull off a narrow victory over the democratic candidate (Johnson?).
So, Nixon comes into office expected to _win_ in Vietnam, not just get "peace with honor" or just get out. The situation is rapidly becoming less popular, but it is not as yet as divisive as it was OTL. What happens?
Bruce