Differentiated integration as symbolic politics? Constitutional differentiation and policy reintegration in core state powers

What are the policy consequences of constitutional differentiation in core state powers? We argue that the most important consequence is not necessarily the exclusion of the constitutional outs from the policies of the ins, but their reintegration by different means. The outs often have strong functional and political incentives to re-join the policies they opted out from, and the ins have good reasons to help them back in. We develop a theoretical framework that derives the incentives for reintegration from the costs of a policy exclusion. We use a novel dataset of reintegration opportunities to map trends and patterns of reintegration across policy fields and member states. We analyze selected cases of reintegration to probe the plausibility of our theoretical argument.