The European Union (EU) through a series of treaties has gradually deepened its institutional powers within member states and widened its membership to 27. These changes were largely pushed forward by political elites relying on permissive consensus. Failed referenda on treaties and declining general support (beginning in 1993 with the entry into force of the Treaty of Maastricht) expose growing public discontent. Previous studies claim that when citizens voted against the Treaty Establishing a Constitution for Europe and the substantively similar Treaty of Lisbon, they did so based not on opposition to the treaties themselves but to something else. Through evaluation of all 27 member states, I reveal that discontent is highest on the question of enlargement. Conclusions in the literature on what explains this opposition are also mixed. Replicating a study conducted by Gabel (1998), I compare the many integration support theories existing in the literature. Using survey responses from Eurobarometers and the European Values Study I establish that citizens are not homogeneous in what determines their views toward enlargement. Attitudes of individuals in original member states are influenced by their level of trust in governmental organizations. Members of the first enlargement base their opinion on the degree of Europeanization of their self-identity. And citizens from the most recent enlargements consider the EU in terms of their attitudes toward national governments.