Institutionalization without moderation? Radical right post-breakthrough adaptation in multilevel Spain. The case of Vox

How do new radical-right parties adapt after their electoral breakthrough to institutionalize within democratic systems? This article examines post-breakthrough adaptation through a longitudinal study of Vox in Spain from 2020 to 2025. Rather than explaining electoral emergence, it conceptualizes institutionalization as a dynamic process shaped by the tension between anti-system rhetoric and the demands of multilevel governance. Using a mixed-methods within-case design that combines qualitative evidence on ideological and organizational change with CIS post-electoral survey data (2019 and 2024), the article identifies three interrelated adaptations. First, Vox recalibrated its ideological profile by reducing the salience of territorial Jacobinism while intensifying a cultural-backlash agenda centered on memory politics, gender, and immigration. Second, the party institutionalized its organization through increased centralization of leadership, candidate selection, membership, and finances, enhancing discipline but generating recurrent internal conflicts. Third, these adaptations translated into pragmatic yet fragile subnational governance participation and voter realignment, marked by declining importance of anti-devolution attitudes and growing support among younger voters, conditional on media exposure. The article shows that institutionalization in decentralized systems may rely less on stable office-holding than on strategic flexibility between institutional participation and oppositional identity.