The establishment of the EU banking union reveals two major shortcomings of liberal intergovernmentalism. First, it fails to explain the preference formation of the most important actor – the German government. The banking sector was divided between public and private banks, and there is no clear‐cut pattern about whose interests the German government promoted. Second, material bargaining power cannot account for German concessions despite favourable power asymmetries. This article seeks to demonstrate how an ideational frame can convincingly fill these gaps. Ordoliberal ideas were constitutive for German preferences. The manipulative use of ideas as strategic resources by the German government's opponents explains why it made significant concessions. Germany's government publicly acknowledged that breaking the ‘vicious circle’ between banks and sovereigns was the main objective of the banking union. This became a rhetorical trap used by a coalition of Southern European member states to force the German government to make concessions.