The Manchurian Candidate
The significance of this movie is complex. I'll try to state it here, but let's note in passing that one take on it is, although (in my experience) very common, obviously too shallow. This is the interpretation that the movie is an indictment of vehement anti-communism which portrays it as deranged. This is too facile because the communists are certainly the villains of the movie and the climax of the movie is the heroic slaying (by Raymond Shaw) of the most powerful communist in the movie, his mother. If you think the take-away message of the film is that one shouldn't be vehemently anti-communist, then consider who the villains of this movie are and consider the profundity of their villainy. But let's leave that aside.
Notice two key elements of the movie: (1.) Raymond Shaw was a man whose spirit was crushed by a wicked mother by age six. Stunningly, he reported that he didn't always hate his mother; at six he only disliked her. As a result, Raymond's psyche could be controlled by his mother and his other enemies. (2.) The communists' "Manchurian" candidate, Johnny Iselin, was supposed to whip the crowd into a frenzy with a speech at the convention, delivered with Iselen covered in the blood of his running mate.
The movie is an allegory about the role of psychological dysfunction in American political life. Dysfunctional relationships amongst intimates, amongst acquaintances, and between politicians and their constituents create and are created by resentment, spite, hatred and rage. These sentiments cause despair, guilt and a resolve to please the bully who created them. One becomes crushed in spirit, nihilistic, lonely, and also one feels guilty over one's debased state and eager to please the bully in order to appease him. Wrongly deciding to appease the one who caused one's resentment, one thinks that being compliant can make everything better, so that there are no hard feelings. This is the dizzy cowardice of the victim who in the face of his oppressor is reduced to officious smiling and fearful paralysis.
The dysfunctional relationships cause narcissistic lives of unhappiness, such as Raymond's. They also cause those involved in them to support political agendas that play upon the their particular derangements. Excitement, resentment, hatred and enthusiasm play too large a role in political life, and this is the reason. These are crippling emotions, and that includes the euphoric sensations of excitement and enthusiasm felt when one contemplates the supposed political answers to one's sicknesses.
The movie, therefore, means this: that American political life is poisoned with shrill, cruel and spiteful pundits and politicians. The voting public is subject to these same emotions, as well as envy, resentment, and anger. The political forum in this country is in substantial measure a feedback loop between the politicians and the voters, in which the former stir the latter into action by directing these animating forces at specific political targets. Raymond's mother did this just as surely as Hitler did. Many contemporary politicians and pundits do it today, although not to such an exaggerated degree.
This is the point of the movie: that members of our democracy can be made to choose governments by appealing to their hypnotic states of resentment and hatred. At one point, a character in the movie asks, Can a hypnotic subject be made to do what he would, upon calm reflection and in a cool hour, recognize as immoral? Yes. When the deranged emotions bring one to one's political stances, things go awry.
The crucial cultural component of our political system is virtue and virtue is incompatible with these crippling hypnotic states. A virtuous member of our political system will be courageous, calm, never spiteful or hateful. He will have the fortitude to stand up to evil. He will not hold grudges but instead will forgive those lured by others into a state of crippling hatred. He will act so as to protect liberty and keep power from being concentrated in one place - the government - where it is more easily taken by the wicked. He will lead others to this sort of character, as well (because he loves people and love is guidance toward character.) In the movie, the Jordans - father and daughter - were such people. They transformed Raymond by their love, but the enemy retaliated, to devastating effect. Even the noble and good such as they need to know about the effects of hypnotic debilitation in order to effect a complete rescue of its victims.
UPDATE: I am speaking here of the 1962 movie directed by John Frankenheimer. I have not seen the 2004 remake. As for Richard Condon's book, I have never read it, although I will soon do so.