Replication Data for: Why accommodate? How niche pressure and intra-party divisions shape mainstream party strategies

Research demonstrates that mainstream parties often take up the issues and positions of emerging Eurosceptic and anti-immigration parties. Yet, these accommodative strategies generally do not pay off. Why do mainstream parties nevertheless accommodate these niche actors? I argue that mainstream-niche competition is governed by intra-party dynamics. The pressure exerted by niche parties alone does not suffice to drive internally united mainstream parties to accommodate. However, when mainstream parties face substantial intra-party divisions on the niche party’s issue, they may yield under internal pressure. I find empirical support for my theoretical claims on the issue of European integration using expert survey data on 78 mainstream parties in 14 Western European democracies between 1999 and 2019. The findings contribute to our understanding of the conditions under which niche parties are contagious and illustrate how intra-party divisions can steer parties away from vote-seeking strategies with consequences for voter representation.