Among the states/nations represented at the convention are: Panem, iOwa, eHio, Svalbard, Skyrim, Belarus, Kardashistan, Electrochussetts, L'oihi, R'lyeh, New New York, Waterworld, the Tri-State Area, Old Zealand, and (the Lost City of) Atlanta. The latter was featured in the previous episode "The Deep South" (2000) and is entirely populated with redneck merpeople.
Nixon's head promises to build a "Dyson Fence" to keep illegal aliens away from Earth. This is a reference to a Dyson Sphere, a hypothetical spherical structure which surrounds a star with beings living on its inner surface.
At the convention segment of the episode, someone can be seen holding a sign which says Panem, a reference to the Hunger Games series.
The character of senator Travers was specifically designed as a reference to Barack Obama: he is from Hawaii, has Kenyan parents, has a foreign-sounding middle name, and has to show a birth certificate to prove that he is not an alien.
Because Chris Travers succeeded in changing the time line, the future in which he came from no longer exists, and thus he starts disappearing. When the time line reverts back to the original, it creates the circumstances that caused him to travel back in time in the first place. Since this is a self-contained time-loop paradox, it meets the requirements of the paradox-correcting time code.