A Bright Shining Lie (movie, 1998)

Something in his past keeps career Army man John Paul Vann from advancing past colonel. He views being sent to Vietnam as part of the US military advisory force a stepping stone to promotion. However, he disagrees vocally (and on the record) with the way the war is being run and is forced to leave the military. Returning to Vietnam as a civilian working with the Army, he comes to despise some South Vietnamese officers while he takes charge of some of the U.S. forces and continues his liaisons with Vietnamese women.