“The campaign against subversion redrew the boundaries of acceptable Democratic liberalism to exclude both Communists and those willing to cooperate with them.” Professor Eric Foner
Political beliefs in this country run the whole gamut from the far right to the far left, but most Americans hold views that are fairly close to the center. The political mainstream includes people who differ with each other on important political issues, but continue to see themselves as loyal Americans, and endorse and support our current constitutional form of government.
People on the radical fringes make up a very small minority of the America population, but they tend to put themselves in positions of influence in government, in the media, and especially in academia. College faculties attract left wing extremists the way a picnic attracts ants, and history faculties, for whatever reason, appear to have an especially strong appeal for radicals.