Party identification is known to influence almost all aspects of political life. How this attachment develops across the adult life cycle, however, remains unknown. I argue that people reinforce their partisan predispositions by voting for their preferred party. Voting entails a choice over a set of alternatives. This choice is likely to induce rationalization. In so doing, it provides signals of group identity, which in turn strengthens people's partisan ties. Testing this hypothesis is made difficult because it implies a reciprocal relationship between partisanship and vote choice. I address this problem by using vote eligibility as an instrument of vote in a sample of almost equally aged respondents. The results indicate that elections fortify prior partisan orientations. Moreover, they do so not by increasing political information. Rather, it is the act of voting for a party that, itself, bolsters partisan attachment. This act leaves a long-lasting imprint on people's partisan outlooks.