Runoffs, Pluralities, and Distribution Requirements

Presidential systems set different bars for victory, and that bar decides how much of the country a winner actually has to speak for. Under a plurality rule, like Mexico's, whoever gets the most votes wins, period. A candidate could take 38 percent while two rivals split the rest, and that candidate becomes president immediately, no second round needed. Under a majority rule, like Russia's or Iran's, the winner needs more than 50 percent. If nobody clears that bar in round one, the top two finishers go to a second round, a runoff, where one of them is guaranteed to cross 50 percent because it is now a head-to-head race.

Some countries add a distribution requirement on top of a vote threshold, forcing a winner to prove support is spread out, not just concentrated in one region. Nigeria requires a presidential candidate to win at least 25 percent of the vote in two-thirds of its 36 states, plus a plurality nationally. A candidate could lead nationally and still fail to win outright if their support is too regionally lopsided, triggering a runoff.

These rules sit right next to how legislative seats get distributed, because the same logic, how much agreement a system demands before handing over power, shapes both. Plurality and winner take all rules tend to produce fewer, stronger parties and quicker results; majority and distribution rules force broader coalitions and slower, more negotiated outcomes.