Sebastian Stan has joined the ensemble of the 6-hour series "Political Animals," USA Network said Thursday. The cast also includes Sigourney Weaver, Carla Gugino, James Wolk and Brittany Ishibashi. The series is to air this summer on the cable network. Stan will play Thomas "T.J." Hammond, the son of former first lady/newly appointed Secretary of State Elaine Barrish, played by Weaver, and her ex-husband, the former President Bud Hammond, who has not yet been cast. Stan has appeared in the film "Captain America" and TV's "Gossip Girl."