Liberal infiltration refers to the tendency of liberals to try to insinuate themselves into groups of other political ideologies, in order to subvert, slander, or corrupt them. It is a continuing historical phenomena; possibly the first, and most obvious example, being the French Turn advocated by Trotsky during the 1930s, which was a series of peaceful protests and demonstrations by members of various socialist parties attempting to overthrow the fairly and democratically elected governments of Europe at the time, such as in France. It has continued throughout history, with groups such as the so-called 'Christian Identity'  and the Revolutionary Communist Party worming their way into the media and politics. It was this tradition that Senator Joseph McCarthy unsuccessfully attempted to halt in the early 1950s.
- Isaac Deutscher, The Prophet Outcast: Trotsky, 1929-1940.
- An article from the UK Guardian on the subject