Does differentiated integration strengthen the democratic legitimacy of the EU? : evidence from the 2015 Danish opt-out referendum

Since the 1990s, European integration has been characterized by a combination of politicization and differentiation. Starting with the Danish referendum on the Maastricht Treaty in 1992, which has led to a series of Danish opt-outs from the Treaty on European Union, domestic politicization has been one of the major drivers of differentiated integration in the EU. Whereas recent theorizing and research has covered the causes and conditions of differentiated integration extensively and has also addressed some of its institutional effects and dynamics, we lack any empirically based understanding of its micro-level consequences. Does differentiated integration improve the democratic quality of the EU and strengthen citizens’ support – or does it promote political divides and foster citizens’ alienation from European integration? This paper develops a theoretical argument on the positive attitudinal effects of differentiated integration, contending that differentiation accommodates heterogeneous preferences in a diverse EU and strengthens citizens’ ownership of European integration. A quasi-experimental analysis of public opinion of the 2015 Danish Justice and Home Affairs opt-out referendum demonstrates that the public vote increased citizens’ internal EU efficacy, indeed. Eurosceptic voters in particular strengthen their belief that their individual voice counts in EU politics, suggesting that differentiation can have a positive effect on the perceived democratic quality of the EU.