Analyzing ideological disparities in multi-speed membership parties: the case of the Italian Democratic Party

Party organizations are undergoing notable transformations. The existing literature commonly indicates a shift towards participatory models and membership forms that blur the distinction between party members and sympathizers. These transformations have significant implications for internal party unity and coherence. This study examines the ideological cohesion among members, sympathizers, and voters, using the Italian Democratic Party as a case study from 2009 to 2023. Using an original dataset integrating survey data from multiple sources, the article explores ideological shifts among members, sympathizers, and voters over time, highlighting both similarities and differences. The findings reveal that while members and voters differ significantly across all periods, members and sympathizers exhibit substantial ideological convergence in most organizational cycles, diverging only during more center-leaning leadership phases. Moreover, the probability of self-positioning to the left of the party increases as we move from voters to sympathizers, and from voters to members: deeper involvement is associated with a more extreme ideological alignment. All in all, organizational embeddedness influences ideological positioning across membership strata.