Political scientists have long been concerned that a popularly elected presidency may destabilize competitive party systems. We develop and test a new theory holding that the impact is more immediate and severe than previously assumed. Coexisting legislative and presidential coalitions first and foremost impede the evolution of predictable party interactions at the executive level, which is the domain of the cabinet. This quality has become accessible for comparative research thanks to the concept of party system closure. Using a new dataset for all European democracies since 1848, we show that presidential elections undermine party system closure in two ways: (1) by confounding patterns of government formation (notably under powerful presidencies) and (2) by disturbing electoral/legislative politics, which in turn affect executive politics. The former, direct effect emerges as dominant from a series of panel analyses and case illustrations. These findings have important implications for current problems of constitutional design and institutional reform.

An institutionalized party system is often regarded as a precondition for a well-functioning democracy. Recent recesses in democracy and, in particular, in the liberal dimension of democracy in relatively established party systems, however, warrant a fresh look into how party system institutionalization shapes liberal democracy. We use a dataset that covers 58 European party systems over more than a century to assess how party system institutionalization in the governmental arena – closure – is related to more robust liberal democracy. Our results show that stable coalition combinations are conducive to higher levels of liberalism, while infrequent government changes and the exclusion of new parties from the governmental arena have a detrimental role.