This paper introduces national partyism as an alternative explanatory framework for understanding the process of treaty amendments in the Post-Maastricht era. Using data on the issue-specifc positions on the Amsterdam, Nice, and Lisbon intergovernmental conferences, I identify the latent preferences of the political leaders on two dimensions of European integration: the design of governance and the pooling of policy competences. This allows to compare the explanatory power of intergovernmentalism and national partyism for the formation of their preferences, interstate bargains, and institutional choices. The findings suggest that intergovernmentalism still provides important insight into preferred governance design, which reveals a conflict between leaders from large/rich and small/poor countries. Partisan ideology characterizes the preferences for the pooling of policy competences, which helps to find compromise on European integration. In the Post-Maastricht era, interstate bargains are dominated by leaders from small, status quo-prone countries with credible referendum threat.This promotes institutional choices for a system of informal governance with high checks-and-balances, in which responsiveness to voters' interests plays a marginal role.
