The erosion of constitutional tolerance

Constitutional tolerance—the voluntary subordination of member states to EU law—was once the normative hallmark of the European Union’s constitutional order. This hallmark is now eroding: subordination of member states to EU law is in question, and so is its voluntary character. Against this backdrop, the article revisits a long-neglected question: what are the foundations of constitutional tolerance in Europe? Drawing on federal theory, it shows that constitutional tolerance depends on a precarious federal balance between contradictory commitments to unity and diversity. The article argues that the Court of Justice of the European Union is developing article 2 of the Treaty on European Union (TEU) into a judicially enforceable guarantee clause as a means of governing this tension through the defense of a constitutional project shared by the member states. However, this approach is associated with an often-overlooked challenge in the European Union: the member states are characterized by different varieties of constitutionalism, with radically different conceptions of the constitutional ideas set out in article 2 TEU, including democracy and the rule of law. While the judicial enforcement of shared values may serve as a mechanism of constitutional defense, it also risks displacing the federal balance on which constitutional tolerance ultimately depends.