Eastwood plays Frank Horrigan, a secret service agent who keeps thinking back to November 22, 1963, when, as an agent hand-picked by President Kennedy, he became one of the few agents to have lost a president to an assassin.
Decades later, psychotic Mitch Leary (John Malkovich) is stalking another president (Jim Curley) running for re-election. He has spent long hours studying the psyche of Frank Horrigan, and he taunts Horrigan (feeling that there is a bond between them), telling him of his plans to kill the president.
After his conversation with Leary, Horrigan makes sure he is assigned to presidential protection duty. Horrigan has no intention of failing his president this time around, and he is more than willing to take a bullet. But everything goes Leary's way -- he is smart and cagey and the president's aides refuse to alter the itinerary.
As the election draws closer, Horrigan's chances to catch Leary look to be less and less a possibility, and he begins to doubt his own abilities -- both now and in the past, when Kennedy was murdered.