Determinants and effects of inter-candidate endorsements in presidential run-off elections

It is widely assumed that many (non-viable) presidential candidates enter double-ballot elections with the primary aim of bargaining for benefits with the two front-runners in exchange for their endorsement in case of a run-off. While several studies have shown that majority formulae are indeed associated with a higher number of presidential candidates compared to plurality, there is hardly any systematic evidence on the scope of candidate endorsements and their effect on electoral outcomes. In this paper, we use an original data set comprising 179 defeated candidates and 88 run-off competitors in 44 presidential elections across 9 European countries, 1951-2022, to provide a first comparative study of inter-candidate endorsements in presidential elections. We find that about half of the candidates who did not make the run-off endorse a second-round candidate; however, there are notable differences between countries and elections. This variation is partially explained by institutional variables, candidate characteristics and first-round results. We show that an incumbent as runner-up and temporally distant legislative elections decrease the frequency of endorsements and that defeated candidates with higher vote shares have a lowered tendency to support one of the run-off contenders. In addition, our analyses indicate that endorsements matter for electoral outcomes. Run-off candidates who were supported by candidates who cumulatively received a high share of the votes in the first round significantly increased their vote share in the second round. Our findings contribute to the research on the effects of electoral systems and shed light on hitherto under-researched aspects of candidate and voter dynamics in presidential elections.