The McCarran International Security Act of 1950 is real, although the part referenced in the movie (that allows for the detention of people suspected of being security risks) was gutted the year this movie was released.
Much of it is still on the books though, and is used to harass left wing organizations. If memory serves, it’s the reason citizenship tests still ask if you’ve ever been part of a communist organization.
10000%. At the end of the day the law is “whatever you can get away with,” and the people who make the laws can get away with a lot.