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 as such are unlikely cause further fragmentation already regimes. If the decides adopt new treaties and laws response crises, however, these likely reproduce extend pre-existing patterns of differentiation. Empirically, this study offers within-case counterfactual analyses Euro migration crises. Whereas crisis triggered a major institutional change Eurozone, member states could not agree on thorough reform asylum system. Correspondingly, we observe excess but stable crisis.