This article examines whether the electoral success of Eurosceptic challenger parties influences mainstream party positions on European integration. By using Euroscepticism as an independent variable, this article examines whether the emergence of Eurosceptic parties matter for mainstream party positioning. Second, the article gauges whether radical right Eurosceptics have more leverage over mainstream party positions on European integration than radical left parties. Third, it is measured whether mainstream parties are more prone to adjust their EU positions when they are in opposition or have been subject to electoral losses. The findings of the article have important implications for the future course of European integration as they show that marginal actors with a cultural agenda can play an important role in shaping party positions on European integration.
