Losing Office, Switching Sides: Evidence from Spanish Municipal Elections

Abstract

Using data on nearly 190,000 candidates across five Spanish municipal elections (2003–2019), we estimate the causal effect of electoral defeat on party switching. We combine a high-dimensional fixed effects panel model with a regression discontinuity design exploiting the quasi-random assignment of council seats under Spain's closed-list D'Hondt system. Both approaches yield consistent evidence that not securing a council seat is associated with a higher probability of changing party affiliation by 2.1 to 2.3 percentage points—a 13.5% to 14.5% relative increase. Additionally, regression estimates show that party switching is more strongly linked to better future electoral outcomes among non-elected switchers than among candidates who switch while holding a seat. Our results support the theory that politicians are primarily motivated by office-seeking ambitions and highlight the strategic nature of party switching in local politics.