After more than three decades of multiparty elections the Brazilian party system is highly fragmented and party identification among voters is low. Even for politicians parties seem to be empty vessels, an auxiliary tool to organize election campaigns and build support for ruling coalitions. However, close to 10% of voters are registered as party members, which makes Brazilian parties powerful membership organizations, a feature that does not fit the previous characterization of pragmatic, elite driven organizations. This paper examines as to what extent ideological or pragmatic motivations drive citizen to join political parties. We identify a seasonal pattern of new members joining political parties and match this regularity with the electoral calendar, rejecting both hypotheses. However, the boom of influx of new members before election allows inferring that party membership plays an important role for intraparty competition. Potential candidates gather support for running on the party ticket. The analysis is based on a dataset on more than 20 million party members of all political parties, registered with the electoral management body over 10 years. These data provide public information on when members join and leave part organizations. Multivariate regression models support the findings that recruitment of new members is driven by political leaders gathering support for intraparty competition.
