Evidence suggests an accelerating trend toward renationalization of policy in key domains in Europe. This trend presents both dangers and opportunities for Europe and the United States. For the United States, a nimble policy toward Europe will be essential. The United States has always worked with individual national governments in Europe and has been accused of not embracing the fullness of European integration in the European Union. America will have to acknowledge the competence of the EU in some domains even as it recognizes that other areas require more intensive cooperation with individual nations. For Europe, many see the return of national purpose as a route to irrelevance on the global scene. So it may be. But if renationalization can be turned into a more roundly supported and authentic set of purposes, Europe could find itself well positioned to play a stronger role in the world as a whole than it has been able to muster for itself in recent decades. The return of constructive nationalism, among nations with well-defined rules of cooperation, might paradoxically energize Europe in ways that Brussels has not been able to achieve.