["JCMS: Journal of Common Market Studies, EarlyView. ", "\nAbstract\nMost classical theories of European integration look at internal mechanisms of polity formation (e.g., spillovers between policies for functionalism, increasing returns for institutionalism, public opinion for postfunctionalism, etc.). However, external mechanisms of polity formation are not as central in European integration theories except in the Europeanist extension of the bellicist theory and the crises literature. In this article, we further develop and decompose the latter approach through the lens of public opinion by investigating the impact of perceived threats and economic vulnerability. We exploit an original three‐wave panel survey fielded in seven countries during the Russian invasion of Ukraine, allowing us to explore the evolution and impact of such threats as the crisis unfolds. We hypothesise that the effects of threat and economic vulnerability on preferences for polity formation are moderated by satisfaction with policy and ideology. Our results show that threat, but not vulnerability, has a strong effect on support for a European Union army. Importantly, the effect of threat is moderated to a considerable degree by ideology and satisfaction with policy."]