Think of the great time comedians have had mocking and imitating every modern president since the early 70’s. Nixon’s speech patterns, body gestures and criminality, Ford’s clumsiness, Carter’s charming yokel demeanor, Reagan’s jellybean fetish and overall idiocy, Bush the Smarter’s voice and malapropisms, Clinton’s overt cockiness, and Bush the Lesser’s utter cluelessness. And then there’s McCain, Palin, Gore, who seems to satirize himself more than other’s do (see 30 Rock and other shows he’s appeared in), Quayle, and Dole. Paul Waldman explains why Obama is so difficult to parody and why there really aren’t any good comedic acts that are able to mock him and Biden. And you can see why from his performance at this year’s correspondent’s dinner.