Back to the subject matter at hand, I think that there would a more or less instant discrediting of whatever group conspired to kill the President, or more likely the kinds of political groups that inspired them. Let's say, for the moment, that Kennedy had been killed by some group of ultraconservative John Birch supporters, as opposed to a communist ex-defector. You know, people ideologically in agreement with the people who passed around "Wanted for Treason" posters. I'm presuming the idea here is a small conspiracy, of around four or five at the most people involved. I think the fact that there was a conspiracy, or at least two different shooters, would be very clear relatively quickly, depending on how many shots end up being fired. I'm presuming a two gunman scenario because that's the difference most OTL Kennedy conspiracy theories are predicated on. Very rarely do you here a conspiratorial single gunman scenario, though they do exist. Anyway, back to the point. A conspiracy would probably have some degree of advanced planning involved. And more likely than not, someone in the conspiracy would be able to drive, which Oswald couldn't. So, there's a good chance at least some of the members of the conspiracy will be able to leave Dallas. Again I presuming a great deal of convergence, so bear with me. I think there's a high chance that at least one of the gunman is going to leave evidence of himself behind, which can probably be traced back to him relatively quickly. There would probably be some kind of national fixation approaching a sense of panic during the initial manhunt. One of the members would be arrested, he breaks under interrogation. Through extradition the other members of the plot are quickly arrested. When it becomes clear precisely why these people killed the President, you'd have an almost instant discrediting guilt by association effect going on I'd suspect for ultra conservative groups in the United States. The "Dallas Five" are quickly convicted, and the assassins themselves receive the death penalty. Goldwater might have to do damage control to disassociate his brand of conservatism from the "Dallas Five" but in the midst of the anti-Bircher backlash, I think Goldwater would probably stay out of alt-1964, while stressing his condemnation of Kennedy's killers. That means that Johnson crushes Nelson Rockefeller in the general election. I suspect that in this world the Kennedy assassination, aside from its historical impact, is something like a very early version of the Oklahoma City bombing. It would a demonstration that ultra conservative political paranoids can be dangerous. Also, if he plays his cards right, and he isn't permanently, and entirely unfairly, scarred by some guilt by distant association, you might just see a Goldwater Presidency somewhere down the line, since he isn't going to be the candidate in 1964. I'm not sure how plausible my scenario is, since it assumes some degree of competence among the conspirators, which isn't guaranteed.