The challenger advantage – how challenger parties disrupt mainstream party dominance in the European Parliament.

Under what conditions can challenger parties disrupt mainstream party dominance in democratic institutions? While extant work describes the cultural and economic developments that benefit challengers and parties’ programmatic responses to these, I demonstrate <italic>when</italic> and <italic>how</italic> challengers exploit these conditions in their political communication. Theoretically, I posit that challenger parties have relatively stronger vote-seeking incentives than mainstream parties. These collective incentives affect individual parliamentarians’ cost–benefit calculations. Challenger parliamentarians will engage in anti-establishment rhetoric and issue-entrepreneurship when these signals are more likely to reach the voting public and pay-off electorally. I test this theory by analysing parliamentary debates from the European Parliament (1999–2016) through a novel combination of word embeddings and bespoke dictionaries. I find that challenger parties indeed pursue different communication strategies than mainstream parties. Challenger parliamentarians engage in anti-establishment rhetoric in the run-up to elections and issue-entrepreneurship during crises. This is because these factors make speeches more likely to be transmitted to voters. These results demonstrate that challengers adjust their political communication in opportune moments giving them a competitive advantage over less flexible mainstream parties. [ABSTRACT FROM AUTHOR]