I saw this first-hand at a Canadian college in the late 60's. The college was new and it recruited a lot of professors, many of whom were Marxists. These professors established themselves in the political science, sociology, and athropology departments. They also hired their Marxist graduate students who served as tutors. In a very short time, these departments served as Marxist bulwarks, and their students as a substantial band of trouble-makers who kept the campus in turmoil for several years.