How NM, do you see the PCF fitting in? Obviously they accommodated the existing power structures of the 3rd and 4th Republics (running lots of municipalities, communes and a good few Departments) but did not seem to change their rhetoric much --- until I suppose the 1980s.
Their movement into government either caused (or was coincidental) with a long slow decline as the PS and the FN nibbled away at their supporters until the old industrial strongholds of Nord, Pas de Calais, Marsailles Red Paris and the like were pretty much gone. Their support now -- such that it is (although of course the CPGB would love to have had similar support that the PCF has now) -- seems to be in the old rural bastions of Limosin etc.
Its a curious case I think! What is your view? I am curious.