Inflation or Moderation? Presidential Runoffs, Legislative Party Systems, and Coalitions

Nearly half of the world’s presidential democracies choose their chief executives using a majority-runoff electoral rule (MRO), while most others used single-round plurality. What difference does it make? On the one hand, critics of MRO assert that the lower threshold of the first round inflates the number of presidential candidates, and with it the size of the party system. A fragmented party system, in turn, can make presidential coalition building difficult and volatile, which can cause policy stagnation and threaten democratic stability. On the other hand, advocates of MRO argue that is more likely to produce moderation in policy making. In the second-round, candidates must compete to assemble a majority coalition, so they will appeal to the median voter. Plurality elections, by contrast, can be won with smaller, more extreme coalitions of interests. Early studies claimed confirmation of the party system inflation effect. We take advantage of an additional 15 years worth of electoral data and find that party system inflation under MRO has diminished considerably over time, presumably as a consequence of voters and parties learning how best to operate under MRO rules. We conclude by focusing on the suggested ‘good side’ of MRO: policy moderation. We show that among the large number of leftist presidencies in recent Latin American politics, MRO systems tend to produce moderate social democratic presidencies, while single-round, plurality-rule elections beget nearly all of the radical neopopulist presidencies, arguably much greater threats to democracy than a slightly larger number of parties.