In Futurama, President Nixon's head gets to be president again, this time of all of Earth, and is later often seen with the headless clone of Spiro Agnew. Spiro Agnew was Nixon's vice president from 1969 to 1973. Nixon's presidency was both before my time, and in a different country. As such, I don't get why Futurama brought him back as a headless clone.
What was the joke behind the headless clone of Spiro Agnew?