Cascading opt-outs? The effect of the Euro and migration crises on differentiated integration in the European Union

Do integration crises reinforce legal differentiation in European integration? Are differentiated EU policies under stress prone to cascading opt-outs? We argue that integration crises as such are unlikely to cause further fragmentation in already differentiated EU regimes. If the EU decides to adopt new treaties and laws in response to the crises, however, these are likely to reproduce and extend pre-existing patterns of differentiation. Empirically, this study offers within-case counterfactual analyses of differentiation in the Euro and the migration crises. Whereas the Euro crisis triggered a major institutional change in the Eurozone, the member states could not agree on a thorough reform of the asylum system. Correspondingly, we observe excess differentiation in the Euro crisis but stable differentiation in the migration crisis.