The Sentinel (2006)

The veteran agent of the American secret service Pete Garrison saved the life of president Ronald Reagan in the past and became a legend. Presently he is responsible for the personal security of the American president Ballentine and the first lady Sarah Ballentine, with whom he is having a love affair. When his informer Walter discloses that there is a traitor in the secret service and a plot to kill the president, his former friend David Breckinridge and the chief of the secret service William Montrose are in charge of the investigation and all the agents are submitted to a polygraph test. Due to his situation with Sarah, he is compromised with the results and accused of treachery. He escapes, and in spite of chased by the secret service, he conducts his own investigation trying to find the responsible. [imdb]