DBWI: What if LBJ had dropped out of the 1968 presidential race?

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While perusing Wikipedia earlier, I stumbled upon an interesting tibdit about the 1968 Presidential Election...

...In addition, Johnson was concerned that he might be unable to unite the Democrats in time for the 1968 Presidential Election, and strongly considered dropping out of the race. However, he ultimately decided against doing so...

What would be the possible results of LBJ dropping out in '68? OTL, we saw Eugene McCarthy win a few primaries against him, but without him in the spotlight, does that mean McCarthy is the candidate? Or does someone like RFK (who would only have run if LBJ wasn't in the race...) or Humphrey take the nomination?

What about the general election? Is it a squeaker for the Democrats like it was with Johnson, or does Nixon (or any other Republican in his place) win not just the popular vote, but the electoral vote, as well?