Winter Kills (1979)

Nineteen years after President Timothy Kegan (John Warner) was assassinated, his brother Nick (Jeff Bridges) discovers a dying man claiming to have been the gunman. While trying to avoid his wealthy and domineering father's attempts to control his actions, Nick follows the clues that have been handed to him. As he progresses, it becomes increasingly difficult to discern the real trails from the dead ends, and increasing dangerous as unknown parties try to stop Nick from uncovering the truth.