If You Could Change the Winner of One Presidential Primary Cycle in Recent Primary History, Which Would It Be?

By "recent primary history" I essentially mean between now (2012) and the late 1960s/early 1970s (when party primaries became binding and not just suggestive. If you could change the winner of one party's presidential primary cycle at any point in that frame of time, which would you change, and who would you pick as the winner instead?