["JCMS: Journal of Common Market Studies, EarlyView. ", "\nAbstract\nThe 2015 migration crisis produced partial path divergence within the Schengen Area rather than the supranational upgrading predicted by neofunctionalist theory. Instead of deeper communitarization, the crisis generated institutional asymmetries in responsibility allocation that fractured mutual trust and rendered automatic functional integration unsustainable in a policy domain marked by low transnational interdependence and high identity salience. This article argues that these asymmetries positioned solidarity as the indispensable mechanism through which the European Union transitioned from neofunctionalist automaticity to a postfunctionalist equilibrium of negotiated burden‐sharing. Employing a hybrid theoretical framework that integrates neofunctionalism, liberal intergovernmentalism and postfunctionalism with historical institutionalism and doctrinal legal analysis, the study demonstrates that the 2024 New Pact on Migration and Asylum reorganized and stabilized the Dublin logic. Methodologically, the study adopts a qualitative design combining theoretical reconstruction, historical institutionalism and doctrinal legal analysis. Solidarity is reconceptualized under Article 80 of the Treaty on the Functioning of the European Union as a bifurcated constitutional principle operating simultaneously through flexible interstate responsibility‐sharing and external migration–management partnerships with third countries. This dual structure transforms solidarity into a systemic governance technology that mitigates politicization, addresses path‐dependent asymmetries and preserves the viability of free movement, whilst refining integration theory and advancing a normative understanding of its constitutional role in European Union migration law."]