JFK would win but the GOP would run someone more credible so the GOP loses by a smaller margin.
Goldwater is very much credible. OTOH, he isn't exactly the most electable candidate, especially not in 1964.... (BTW Straha, don't presume Goldwater is that bad of a dude in your book. For one thing, he was both pro-legal-abortion and pro-gays-in-the-military... not traditional conservative positions).
JFK still wins. He's more charismatic than Goldwater, Vietnam wouldn't be biting him in the rear yet, and he will be perceived as being more moderate than Goldwater (a claim with some merit but not entirely true).
It will be a smaller margin, however. Goldwater and JFK were friends, so there won't be as much vicious rhetoric (I don't see the daisy commercial - Karl Rove has nothing on LBJ's canniness or ruthlessness! - coming in this alt-history). Also, no assassination-sympathy vote.
Goldwater wins most of the traditional-republican states that went for Johnson in our '64 election (like the Plains), plus most of the South. He loses about as badly as Bob Dole in 1996, I'd say.
