Generate a summary in one sentence for the following document.

This paper takes up the familiar question of how one can explain support for European integration. One line of explanation builds on trade theory to theorize a calculus of economic costs and benefits. A second explanation draws on cognitive and social psychology to assess how individuals use political cues-grounded in ideology or elite communication-as a guide to complex issues. A third line draws on the psychology of group membership to consider how group identities, above all, national identities, bear on support for European integration. We use multi-level analysis to evaluate these explanations, and we conclude that perceptions of national identity are by far most powerful in structuring views on European integration. We find that the particular perception of national identity matters, as well as how identity is mobilized in national contexts. Thus, while strong national identity is consistent with support for European integration, exclusive national identity is a powerful brake on support. The effect of exclusive national identity varies across countries. It is strongest in countries where referenda on European integration have taken place. Referenda exacerbate conflicts within and among elites and empower single-issue anti-European protest movements, and this mobilizes exclusive national identity in an anti-European direction. Make sure to only use capital letters in your entire response.
user