Everyone remembers the ruckus that erupted when Lionel Jospin's Trotskyist past was revealed. Jospin was accused of practicing the entrisme advocated by the Lambertiste wing of the Trotskyists, penetrating mainstream institutions while continuing to support revolutionary aims. In Jospin's case the charge was false.
Guy Birenbaum today suggests that Patrick Buisson, a close advisor of Sarkozy's, may be an entriste of the Front National. It's no secret that Buisson comes from the extreme right, but Birenbaum has uncovered a difficult-to-find book that shows how close he once was to Jean-Marie Le Pen. The account of the search for the book is over-dramatized, and there may be less here than meets the eye, but you should read the article in any case.