In a new guest column on Sabato’s Crystal ball, Thomas Schaller, professor of political science, discusses President Obama’s campaign message a year from now at the Democratic National Convention in Charlotte in a new guest column on Sabato’s Crystal Ball. “However good the field of potential Republican challengers may or may not be… winning reelection will not be easy,” argues Schaller. He suggests, “in order to win President Obama is going to have to go negative.” As for his campaign message, Schaller predicts, “Obama is most likely to frame his election as an appeal for four more years because the …