This article analyses the gravity and reasons for the crisis currently affecting the French Socialist Party. Going beyond the electoral disasters of 2014, it situates this crisis within the context of the destabilisation of the French party system due to growing divisions on the left and on the right caused by the evolution of the European Union in the current context of economic crisis. The left/right cleavage that structures the functioning of the political system is being called into question by an alternative cleavage that increasingly opposes the supporters of European integration against their opponents. The cross-cutting nature of these two cleavages will henceforth prevent the left from uniting on a programme of government. Within the Socialist Party itself this phenomenon is a factor of serious division and, as a result, makes the government's parliamentary base more fragile. It further deepens the long-standing differences on economic policy because of the explicit choice made by the Socialist government in favour of a supply-side approach. The Socialist Party seems to have arrived at the end of a political cycle where it will have to make choices that it has postponed for many years, with the risk of breaking up and with the threat of starting an electoral and political decline that could ultimately deprive it of its status as a party of government.
