Ernst Haas initially formulated neofunctionalism as a theory of incremental regional polity formation, treating crises as anomalies. Subsequent revisions of the theory incorporated crises as recurring phenomena. This paper introduces a novel conceptualisation and analysis of recent European Union crises, framing them as effects of and challenges to its regulatory polity. It distinguishes between 'failures' and 'attacks', aligning them with the capacity and community-building dimensions of polity formation. Failures, rooted in capacity deficits, prompt capacity development to sustain common policies, varying with international interdependence among member states. In contrast, attacks arise from contestations of constitutive values, necessitating community demarcation through enhanced unity among defenders and exclusion of attackers. The speed and scope of demarcation depend on the attacker's membership position. Through a comparative analysis of the euro, migration, Covid, Brexit, rule of law, and Russia crises, the study illustrates and substantiates its theoretical argument.