THE MANCHURIAN CANDIDATE (1962)

This is a political fantasy involving the Korean War and subversion in the highest level of our electoral process, in it, the son of a prominent U.S. political family is brainwashed into being an unwitting assassin for a Communist conspiracy.
Major Bennett Marco, Sergeant Raymond Shaw, and the rest of their infantry platoon are captured by an elite Soviet commando unit during the Korean War in 1952. They are taken to Manchuria, and brainwashed into believing Shaw saved their lives in combat – for which Shaw is subsequently awarded the Medal of Honor.
Years after the war, Marco, now back in the United States working as an intelligence officer, begins suffering a recurring nightmare in which the seated platoon members are surrounded by a group of sweet little old ladies who had been a part of their brainwashing. One of the ladies tells Sergeant Shaw to murder two of his platoon comrades. The backdrop with the old ladies changes back and forth between them and Chinese/Soviet intelligence officials. When Marco learns that another of the platoon's soldiers has been suffering the exact same nightmare, he starts looking into why this is happening.
Major Marco looks up Sergeant Raymond Shaw and discovers that Shaw's new manservant is someone he recognizes from Korea. Marco and the manservant start fighting in Shaw's house and both are bloodied significantly. Marco is arrested, and when Shaw sees that it is his old major they rekindle their old friendship. Both find love interests: for Marco, it is Rose Cheyney, whom he meets on a train; and for Raymond, it is Jocelyn Jordan, the daughter of Senator Thomas Jordan, a neighbor of Shaw's. Senator Jordan and Shaw's mother do not like each other, but Raymond continues to see Jocelyn.
It is revealed that the Communists have been using Shaw as a sleeper agent who, activated by a post-hypnotic trigger, immediately forgets the assignments he carries out and therefore can never betray the operation either purposely or inadvertently. In Shaw's case, the suggestion that he play solitaire is the trigger. Seeing the queen of diamonds playing card transforms him into an assassin who will kill anyone at whom he is directed. Shaw's KGB handler is his domineering mother, Eleanor (note her resemblance to Hilary Clinton). Married to McCarthy-esque Senator Johnny Iselin, Eleanor has convinced the Communist powers to help install her husband as president and allow them to control the American government through him.
By observing Shaw, Marco discovers the trigger shortly before the national convention of Iselin's political party. He uses the queen of diamonds card to draw out Eleanor's plan: after she obtains the vice presidential nomination for Iselin, Shaw is to shoot the presidential candidate so that Iselin can succeed him. Blaming the killing on the Communists will enable Iselin to assume dictatorial powers. Marco reprograms Shaw, although it is unclear until the final pages whether this is successful. At the convention, Shaw instead shoots and kills his mother and Senator Iselin. Marco is the first person to reach Shaw's sniper nest, getting there just before Shaw turns the gun on himself and commits suicide.