No one ever thought it would be a cakewalk. From that day in January when Johnny Isakson announced he would run for the U.S. Senate, Tom Perdue started hammering the north metro congressman. Perdue said Isakson favored abortion. Said he was too moderate - make that liberal. Said he was too close to the Democrats. Said he was a liar and a hypocrite. That was OK at the time. Tom Perdue is a political consultant, not a candidate. ''Brilliant and ruthless,'' The New York Times recently called him. Some observers doubted that consultant Perdue (no relation to Gov. Sonny Perdue)...