The European Union is in crisis, and a major part of this is the increasing political backlash against the free mobility of persons. Probably the most dramatic symptom of this is Brexit, which could result in the stripping of rights or, in some scenarios, even physical expulsion of millions of people, whether Britons living in other EU countries, or EU citizens presently living in Britain. While the vote outcome apparently took policy makers by surprise, it represents a trend to redefine the status of intra-EU migrants in ways which clarify that EU citizenship is not equivalent to citizenship in the host country of residence. Unresolved contradictions between supernationally regulated free mobility and national sovereignty have come to the fore, precipitating political crisis. This is a serious obstacle for the European project, and one which is fundamentally embedded in the design of the European integration. As a social engineering project driven by "spill-over," European integration incentivizes elites to cooperate transnationally, but leaves large portions of national civil society outside this élite consensus. The consequence is that free movement of persons is stuck in a fragmented and variegated regulatory mode in which the social rights of mobile persons are precarious and dependent on market contingencies.