Previous studies of voter turnout have analyzed the socio-economic and demographic factors that drive mobilization. Less attention has been paid to the role of ideology and attitudes in leading people to participate. Studies of European Parliament elections often view them as second-order races. Our study contributes to the existing literature by looking at the effect of attitudes for participation in both EP and national elections. We uncover significant differences between the two. Particularly, we show that ideologues turnout more than centrist voters during EP elections, but not in national ones. Moreover, we show that some salient issues (particularly the economy and attitudes towards Europe) drive this effect (while others, such as immigration, do not). Our results inform why the European Parliament became more polarized, even in absence of significant changes in the overall attitudes of the European publics. Our results also explain why extreme parties can be more successful in EP elections than in national ones. Lastly, our results also show how British Eurosceptic parties made it to the European parliament, despite the fact that Eurosceptics usually participate less in European elections. These results have strong implications for the future of the EU and for the scholarship on turnout and mobilization.