Parliamentarization and the institutionalization of human rights are two processes of constitutionalization in the EU that constitute a puzzle for explanations inspired by both rationalist and constructivist institutionalism. We propose to analyze these processes as strategic action in a community environment: Community actors use the liberal democratic identity, values and norms that constitute the EU’s ethos strategically to put social and moral pressure on those community members that oppose the constitutionalization of the EU. Theoretically, this process will be most effective under conditions of high salience, legitimacy, publicity and resonance. In a Qualitative Comparative Analysis (QCA) of the EU’s constitutional decisions from 1951 to 2004, we show salience to be the by far most relevant condition of constitutionalization in the EU.