Sideshow Bob is actually an eloquent speaker, and is more the psychopathic kinda crazy, not the "Right now, Obama is spying on me through the microwave!"
Just a reminder to our American cousins that in British English, trump means the noise an elephant makes but also to fart: "Sorry I trumped." Donald the Trump is a noisy noxious unwanted thing on the world stage.
JFK doesn't. He never appeared, at least not in any of the episodes before the latest reboot. One can only assume that JFK got assassinated in the Futurama timeline as well, so there wasn't enough of his head to put in a jar.
Lincoln was shot in the back, not the head, so I guess that's how he got there.