If you're of a certain age, you will remember le Programme Commun--depending on your orientation, either the master stroke that enabled the Left finally to break the Gaullist monopoly on power in the Fifth Republic or the perfidious alliance of "Socialo-Communists" that brought the Cold War enemy into the fortress of power (eventually annihilating that enemy in a reversal of the Trojan horse metaphor). Now there is a book about "l'union sans unité."
Its most avid readers may well be on the Right, however, because the opportunities for a "political recomposition" of the sort that Mitterrand effected in the 1970s now lie on the other side of the political spectrum. Now it is the Front National rather than the Communist Party that lies outside "the republican consensus," and it is the "republican Right," first under Sarkozy and now even more nakedly under its new leader Jean-François Copé, that would like to reinforce itself by bringing in (and to heel) its once-taboo nemesis.
There is a difference, however. The PCF in the 70s was an aging party that was not replenishing its ranks with new young blood. The FN is energetically--and apparently successfully--recruiting young people, as the surprisingly good performance of a 23-yr-old candidate in Villeneuve-sur-Lot shows. The dynamism of the FN among young people aged 20-40 has to be a concern for the UMP. Demographics turned the Common Program into an instrument for defanging the PCF, but demographics may work in the opposite direction if the UMP attempts to make common cause with the FN.