Play to your strengths: Incumbency effect and issue emphasis in Brazilian local elections

Incumbents’ reputations acquired during their time in office influence voters’ choices. Some studies suggest that, when designing their campaign messages, incumbents may benefit from playing to their strengths and emphasizing fewer issues than challengers. In this paper, I provide causal empirical evidence on this behavior using data from Brazilian mayoral elections and a regression discontinuity design. The findings indicate that marginal incumbents — those elected by a small vote margin — produce more concentrated campaign manifestos than challengers who narrowly lost. Moreover, incumbents belonging to cohesive and programmatic parties tend to emphasize party-specific issues more strongly, suggesting that reputation plays an important role in issue selection. To measure issue emphasis and manifesto concentration, I leverage a unique database of more than 28,000 political manifestos and apply a Latent Dirichlet Allocation (LDA) algorithm to estimate a vector of topics—or the issues emphasized by each candidate. Using this information, I calculate Herfindahl–Hirschman indices (HHI) to assess the degree of issue concentration in campaign manifestos.