Complex sentence: The two are finally saved when a Secret Service sniper recognizes them as the real President's Kramer and Douglas and decides to disobey orders to shoot them, and instead shoots Tanner, who is himself about to shoot the ex-Presidents.
Split into simpler sentences: The two are finally saved when a Secret Service sniper recognizes them as the real Presidents Kramer and Douglas and decides to disobey orders to shoot them. Instead, he shoots Tanner, who is himself about to shoot the ex-Presidents.