The title is misleading, unfortunately, because I want to emphasize a long-term effect rather than a PoD. Let's say that during the Republican National Convention in 1980, the Reagan/Ford ticket manages to make it through, and the "co-presidency" becomes a reality, and though Reagan is largely credited with the cultural, social and political shifts, the perception into the next election is that Ford's high level of power has set a new precedent.
While there would definitely be some butterflies, the biggest shift would probably really be that come 1988, Bush - who might still mount a campaign - would not have the advantage of being an incumbent vice president, even if he was appointed to the cabinet in the meantime, making it a comparatively open field. This would have HUGE butterflies for vice presidential vetting in future elections, including 1988 as well as likely even current elections.
So basically, what are the long-term butterflies of a co-presidency becoming the norm?
While there would definitely be some butterflies, the biggest shift would probably really be that come 1988, Bush - who might still mount a campaign - would not have the advantage of being an incumbent vice president, even if he was appointed to the cabinet in the meantime, making it a comparatively open field. This would have HUGE butterflies for vice presidential vetting in future elections, including 1988 as well as likely even current elections.
So basically, what are the long-term butterflies of a co-presidency becoming the norm?