Hmmm! Running in 1984 against a popular Reagan might not be such a good thing for Glenn. Remember Reagan only lost D.C. and Minnesota, thats rather impressive. I really dont know if Glenn would have been able to stop a Reagan victory, he could probably snatch a few more states though.
What if he didn't fall in the shower in 1980 and went on to wrestle the democratic nomination from Carter? We could see the Democrats being split between those who support Carter and those who support Glenn, but lets assume Carter accepts his ousting and throws his weight behind Glenn, just for the sake of the timeline. It is possible he could have defeated Reagan in 1980.
Perhaps the Democratic ticket will be John Carter/Jerry Brown -vs- Ronald Reagan/George H.W. Bush or Bob Dole.