Okay one big reason, you don't have to go further then Hitler. The "cause" to his power was because of the political failure of the Wiemar Public which was imposed on Germany in 1919.
Hope I got it correct!
Between 1946 and 1954, the House Committee of Un-American Activities and Senator Joseph McCarthy attracted public attention by investigating 1. allegations of communist influences in government. HUAC, as the committee was called, investigate claims of communist ties not only in the government, but in other industries as well such as the filmmaking industry in Hollywood.
