It was a key institution in the era of the Cold War, tightening alien exclusion and deportation laws and allowing for the detention of dangerous, disloyal, or subversive persons in times of war or "internal security emergency". The Democratic-controlled Congress overrode President Harry S. Truman's veto to pass this bill. Truman called the bill "the greatest danger to freedom of speech, press, and assembly since the Alien and Sedition Laws of 1798."
Much of the Act has been repealed, but some portions remain intact. For example, violation of Section 797 of Title 50, United States Code (Section 21 of "the Internal Security Act of 1950"), which concerns security of military bases and other sensitive installations, may be punishable by a prison term of up to one year.