Fluctuating Challengerness: the Evolution of Challenger Parties' Programmatic Strategies

European party systems have been shaken by the growing emergence of new actors, which challenge those parties occupying a core position within their national party systems. Challenger parties are those actors struggling to alter the main dimensions of the political competition within their national party system; whereas, core parties are the ones fighting to preserve intact the existing lines of political conflict. The current contribution conceptualizes challenger parties assessing their ability to i) introduce issues neglected by their competitors, ii) politicize the positional extremes of the left/right dimension and iii) adopt an anti-establishment strategy in challenging the metapolitical values of a given party system. The responses – and the patterns of interactions – displayed by the core parties in contrasting the rise of the challengers strongly differed across Europe. I argue that parties should be more likely to shift from a challenger to integrated status in response to an electoral loss. However, the parties’ lifecycle and their degree of integration within their national party system affect the patterns of their moderation strategies. Employing MARPOR data and a new expert-survey on Anti-Establishment Rhetoric, I operationalize the concept of challenger party both in Western and Eastern European countries. This framework allows locating challenger and integrated parties in a continuum, explaining – on the basis of the parties’ characteristics – the potential outcomes of their interactions. Moreover, it conceptualizes for the first time the multi-dimensionality of the challenges that a party can address against the existing systemic equilibria