Strategic campaign communication in single- vs. two-round elections: evidence from candidate manifestos in Brazilian municipalities

Electoral rules shape the strategic incentives of politicians. This paper examines how candidates adjust their campaign behavior when competing in two-round versus singleround elections. Building on the canonical Hotelling–Downs framework, I develop a simple theoretical model with three candidates. It shows that single-round plurality elections generate polarizing incentives, while introducing an adjustment cost between rounds produces a centripetal force toward the median voter in two-round races. To test this prediction, I explore a novel dataset of over 54,000 candidate manifestos from Brazilian mayoral elections (2012–2024). Through supervised text analysis, I construct an ideological score for each manifesto and implement a regression discontinuity design that exploits the institutional cutoff at 200,000 registered voters that determines whether municipalities adopt single- or two-round systems. The empirical evidence supports the model’s predictions: candidates in runoff elections produce significantly less polarized manifestos and choose platforms closer to their competitors’. This effect is driven by the adjustment of campaign rhetoric by candidates whose expected position in the election ranking is third.