Complex sentence: He enjoyed another film success in "The Girl Can't Help It" (1956) opposite Jayne Mansfield, but as his film and theater careers seemed to have reached their peaks, he turned his attention to television.
Split into simpler sentences: He enjoyed another film success in "The Girl Can't Help It" (1956) opposite Jayne Mansfield. However, as his film and theater careers seemed to have reached their peaks, he turned his attention to television.