Turns out there's an author out there who claims that McGovern did father a child while a teenager training for the Army Air Force. George and his wife were afraid during the last month of the 1972 campaign that his secret would come out. It never did. The cynic in me thinks that Richard Nixon's people knew they had won and thus declined to sling that particular bit of mud. If the race had been closer? Who knows.
As I said - just an interesting "what if" bit of history now.