NBC News is staying in-house in its effort to turn around the "Today" show. The network on Wednesday appointed a 23-year veteran of the morning news show as its new executive producer. Don Nash began working for "Today" as a production assistant in NBC's Burbank office in 1989 and will now run the four-hour broadcast. Mr. Nash was most recently senior broadcast producer in the show's control room. He replaces Jim Bell, who shifted to NBC Sports to run its Olympics broadcasts. After nearly two decades of dominance, "Today" has slipped behind ABC's "Good Morning America" in the ratings. NBC also added another layer of management for the show, appointing Alexandra Wallace as the network's executive in charge of the program.