The increasing popularity of European populist radical right parties (PRRs) has often been argued as either a corrective or threat to democracy. In this study, we provide empirical scrutiny to these opposing claims and investigate the impact of successful PRRs on levels of voter turnout. We argue that the emergence of successful PRRs may either foster voter turnout, because they are passionate mobilizers that fulfill a watchdog function and re-introduce electoral competition; or inhibit voter turnout, because they introduce a more negative, hardened tone to politics that further triggers distrust towards politics, politicians and democracy. To investigate these possibilities, we examine whether various societal groups are affected by the emergence of successful PRRs. Using the six available waves of the European Social Survey for the period 2002-2012, we apply hierarchical fixed effect models to test the (de)mobilization potential of PRRs in 19 Western and 14 Eastern European countries. Our results suggest that the emergence of successful PRRs lowers the voting propensity of Eastern European citizens - in particular the young and those with positive attitudes towards immigrants. Whereas in Western Europe, the emergence of successful PRRs increases the propensity to go to the polls among higher educated, more politically interested citizens. The East European results are consistent with theories that those most likely to be affected by the negative campaigning of PRRs - those that oppose PRR ideology and those less politically experienced - will be less likely to turnout in response to the emergence of a successful PRR. The Western European results are consistent with theories that it is those who strongly oppose PRRs that will be motivated to turnout as a result of the emergence of a successful PRR.