Backlash policy diffusion to populists in power.

We analyze how parties respond programmatically to populist parties in power abroad. Political parties often copy the policies of governing parties in other countries-a phenomenon that contributes to waves of transnational policy diffusion. We report the first large-scale comparative study showing that populist parties in government abroad trigger the opposite reaction: instead of inspiring emulation, their highly visible governing dilemmas provoke a policy backlash by parties in other states. We argue that dilemmas arise because populist parties confront unique and debilitating trade-offs between maintaining their anti-system posture and governing effectively, which make them electorally vulnerable. Other parties observe foreign populists' governing dilemmas and respond by distancing themselves in order to avoid these problems. We detect this "foreign populist backlash effect" using spatial econometric analysis, a method that allows us to estimate international policy connections between parties, applied to over 200 European parties' programmatic positions since the 1970s. Our findings illuminate parties' election strategies and show that this backlash effect constrains the spread of populism across Western democracies.