It wasn’t a Carter - Gacy function
the other was a Paul function with his supporters
and he knew Black and his background.
Nice try
Gacy was some sort of local Democratic Party precinct captain in Chicago. Rosalyn Carter came through town on a campaign stop, and Gacy showed up at the event and got his picture snapped.
In fact, you could even make the case that the Carter event organizers knew more about Gacy’s background than the Paul event people did about Black. Gacy’s name was on a list of people who went through Secret Service screening so they could get their picture made with the first lady. There was a minor scandal over it at the Secret Service when Gacy’s serial killing came to light.