"This study compares the explanatory power of intergovernmentalism and national partyism for European integration in the post‐Maastricht era. Using data on the issue‐specific positions of all heads of state and government at the Amsterdam, Nice and Lisbon conferences, I identify a common policy space with latent preferences and outcomes on two integration dimensions, the design of governance and the pooling of policy competences. The findings show that partisan ideology characterizes leaders' preferences for the pooling of policy competences, which helps to find compromise among the leaders from large/rich and small/poor countries on governance design. Due to their credible referendum threat, leaders from smaller countries dominate interstate bargains in the post‐Maastricht era. This implies institutional choices for a separation of powers with a bicameral legislature, which promotes functionalist responsibility at the expense of responsiveness to the concerns of the voters."

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