Art is always looking for taboos to break. And the curious convergence of this summer is assassination. Presidential assassination. “Stephen Sondheim’s Assassins may be closing, but next month, I’m Gonna Kill the President!, a satirical play by the pseudonymous Hieronymous Bang, reopens at a top-secret downtown location. Jonathan Demme has remade The Manchurian Candidate, and Niels Mueller’s drama The Assassination of Richard Nixon, starring Sean Penn, is based on the true story of a salesman who attempts to murder the president. And although the novel won’t be released until August 24 (the eve of the Republican convention), Nicholson Baker’s Checkpoint has already caused a stir: One character ruminates at great length on his desire to assassinate George W. Bush.”