Prime Ministers and Party System Stability in Postcommunist Democracies

abstract: A stable party system is central to making democratic accountability work. Challenges arise from high electoral volatility, reflecting large vote shifts among established parties (within-system) or equally large shifts to new parties (extra-system). Though intriguing patterns of volatility often defy structural and institutional explanations, political agency may be critical for stabilizing party systems, especially in new democracies—or for undermining their consolidation. The authors explore this new theoretical perspective by investigating how prime ministers affect volatility in the paradigmatic case of postcommunist Central and Eastern Europe. Building on a unique data set of prime-ministerial performance in 129 cabinets in eleven countries, quantitative and qualitative analyses demonstrate how agency in the chief executive office shapes the reelection of government parties and the rise of new contenders. Whereas the effect on within-system volatility is immediate, effects on extra-system volatility unfold over time. Hence, executive leadership is key to understanding the dynamics of party-system stability and democratic accountability.