WASHINGTON -- A Democratic senator is blocking Associate Attorney General Robert McCallum's nomination to be ambassador to Australia over allegations he improperly influenced the government's lawsuit against the tobacco industry. In a letter to President Bush, Sen. Dick Durbin of Illinois said it was premature to place McCallum in a new position of trust as long as the Justice Department's Office of Professional Responsibility is conducting an ethics inquiry into the handling of the tobacco case. Any senator may place a hold on an executive branch nominee, an act that can be overcome with 60 votes. The civil racketeering tobacco...