"President Schwarzenegger" was actually a disguised Rainier Wolfcastle
In the Simpsons universe, Arnold Schwarzenegger does end up successful enough to get elected president, but he eventually decides that he's tired of the stress of politics, and he misses his simpler days as an action star. Meanwhile, Rainier Wolfcastle decides that he's tired of being seen as a brainless action star, and wishes that people would take him seriously. One day, he meets Arnold Schwarzenegger by chance, and they both realize how much they resemble each other. Realizing that each has the life that the other wants (a carefree life as a movie star for Arnold, power and respect for Rainier) they switch places à la The Prince and the Pauper. "Russ Cargill" was a member of the Cargill Corporation
A company that is involved in agriculture, pharmaceuticals, risk management, electricity and gas. The company is still owned by the Cargill family.- That, or this movie used him to slip one hell of a Take That! against the Cargill Corporation, (seeing how Russ acted more as a Corrupt Corporate Executive than as an Obstructive Bureaucrat)
Russ Cargill is in fact an alter ego of Hank Scorpio, having infiltrated the USA government.
The entire film is a hallucination created by Grampa
His line "A twisted tail, a thousand eyes, trapped forever, EPA EPA!", said while having a seizure at church seems to refer to Plopper, the mutant squirrel created as a result of Homer placing Plopper's pig crap silo into a lake and the dome respectively. But what if he's not accidentally predicting events shown later in the film? If Milhouse wouldn't have sold out his beliefs, Nelson would have patted him on the shoulder and respectfully left him alone. Instead of punching him.
Just thought it seemed like the kind of subversion the show would do. Colin's family moved away after the movie's events
It'd explain why he hasn't been bought up again beyond a brief cameo. And after an event as bizarre and cataclysmic as the Dome incident, no one would blame Colin's family for wisely deciding to get the hell out of Springfield as soon as they feasibly could.