JOHNSTOWN, Pa. (AP) -- In what was the late U.S. Rep. John Murtha's western Pennsylvania district - reachable through John Murtha Johnstown-Cambria County Airport or John P. Murtha Highway - Democrats watch nervously, hoping his former top aide can hold on to the House seat. Mark Critz, who worked for Murtha for more than a decade in Pennsylvania, including the past three as district director, is in a fierce fight with Republican businessman Tim Burns in the May 18 special election. The national GOP has spent hundreds of thousands of dollars to push Burns' candidacy, sensing a legitimate shot of...