Here was something I was thinking about:
Joe Kennedy Jr. misses out on the doomed flight and requests transfer to the pacific theater, where he earns the Navy Cross and possibly a MOH. It is he, not Jack, that will run for Congress. So young Jack decides to go west and become an actor.
After appearing in numerous war and scifi films, Jack finally gets a break when he is cast in the lead role for Hitchcock's Vertigo. His success there leads to the lead roles in North by Northwest (Roger Thornhill) and Manchurian Candidate (Raymond Shaw), where he earns an academy award as a brainwashed Korean war solider turned assassin. Unfortunately, Joe Jr. is assassinated, and a grief stricken Jack quits film making (as well as buying up the rights to Manchurian Candidate and keeping it off screen for the rest of his life.) His father and brothers manage to convince him to seek an open Senate seat in California, which he is appointed to and is elected to a full term.
On the other side, John Wayne; sickened by the socialism and unAmerican attitudes in pictures (and still angry over Stalin's assassination plot; is drafted by the California Republican party to run against Governor Brown in 1962. Wayne defeats Brown in a landslide, thanks to former Vice President Nixon (who will eventually be elected Senator from New York and then President)
Wayne is reelected in 1966 and 1970, Kennedy in 1970. Wayne plans to retire after his third term, but his plans are put on hold after President Nixon is wounded by Arthur Bremer. Nixon pleads with Wayne to run in his place in '72, as he doesn't want Agnew to succeed him. Wayne agrees, and with Secretary George Romney, wins in a landslide.
Jack is elected Governor in '74, a year where republicans are receiving a shellacking due to a continued war in Vietnam and the outrage over Nixon administration officials and Wayne-Romney campaign workers breaking into the 1972 DNC HQ. His family and the DNC are backing him for the Presidency, but Jack believes Wayne to be too strong. Despite the troubles, Wayne is still admired and supported by much of the country.
Then a bombshell drops.
President Wayne's medical records are leaked to the Washington Post; some going as far back as his first term as Governor. They show he had a cancerous lung removed in secret, and that the President's health is failing.
While trying to be as "politically" sincere as possible, many in the Democratic party and a minority of Republicans are asking Wayne to resign for his own good and the good of the country. Things worsen when members of the President's Secret Service detail gun down four people and wound five others after a woman pulled out an unloaded revolver and when Vice President Romney resigns over expressed doubts of his sanity and his nationality.
Wayne tries in vain to get his selection of nominees to be appointed Vice President: John Connally, Donald Rumsfeld, Jim Rhodes, even Edward Brooke, however must are denied and the rest decline. Wayne takes George H.W. Bush on, but isn't quite sure of whether or not he'll keep him in '76.
Sensing the Duke's weakness, Governor Kennedy runs for the Democrats' nomination, beating the few challengers, and is nominated with New York congresswoman Shirley Chisholm.
And so it comes down to Kennedy/Chisholm vs. Wayne/Westmoreland, with former Senator Eugene McCarthy as a possible spoiler...