Strategic Isolation: The Cordon Sanitaire’s Influence on Coalition Dynamics and Electoral Outcomes in Europe

This study investigates the impact of the Cordon Sanitaire (political ostracism) on coalition dynamics and electoral outcomes in European parliamentary democracies. Despite its widespread adoption since the 1980s, scholarly debate persists about its effectiveness. We develop a spatial voting model differentiating parliamentary and governing coalition medians, analyzing repercussions of Cordon Sanitaire strategies across six European countries from 1945 to 2025. Using ParlGov data, we test two hypotheses: first, implementing a Cordon Sanitaire shifts governing coalition medians away from ostracized parties; second, greater divergence between governing and parliamentary medians increases electoral support for opposing parties. Results robustly confirm both hypotheses, showing a significant shift (13.1%) in governing coalitions away from ostracized parties, and increased opposition support (1.3% per 1% divergence). These findings highlight distinct short-term versus long-term effects: initially successful in marginalizing extremist parties, Cordon Sanitaires eventually strengthen opposition forces. We advise policymakers to reconsider reliance on political ostracism, favoring coalition formation closer to parliamentary medians for enhanced governmental stability and electoral predictability.