Basically what it says on the title.
JFK was shot and killed in November 1963, and LBJ won over Goldwater in a 486/52 landslide just under a year later. But what if Kennedy's health took a nosedive earlier in autumn '63 (he was a very sick man, after all), and by the time Nov 22nd rolls around, he's either resigned from office or dead already? Without the sense of national trauma that came from the assassination, and LBJ's resultant legislative successes such as the Civil Rights Act, is LBJ still able to win a term in his own right, and if so, is it still by as much of an overwhelming margin as OTL?
(For the purposes of this question, I'm assuming that butterflies push Lee Harvey Oswald out of the picture entirely and there's no equivalent assassination attempt on LBJ)