Jim Oberstar and Chip Cravaack didn’t just face each other this morning at the Duluth Entertainment Convention Center Auditorium, they faced angry mobs of their opponent’s supporters. Just seconds into the first comments by DFLer Oberstar, Cravaack supporters began to shout the long-term incumbent down with calls of “liar’’ and “Obama Junior.’’ By the time challenger Cravaack’s turn came, Oberstar supporters responded in kind. Moderators asked for civility and respect, but the cat calls and jeering from a nearly-full auditorium continued through most of the 90-minute forum, often drowning-out candidate’s answers over a faulty sound system that lacked volume. Oberstar...