By allowing for plurality victories in a three-party system, Mexico faces political instability at the federal level continuing long after the July 1, 2012 presidential election. Indeed, Mexico regularly has non-majority outcomes with controversy over potential "spoiling" of the result. The last candidate to win a majority of ballots cast was Carlos Salinas in 1988, and his tally is widely suspected of having been inflated through government fraud.

Mexico has held regular presidential elections every six years since strongman Lázaro Cárdenas came to power in 1934 under the banner of the National Revolutionary Party (PNR). The PNR went through two name changes afterward, eventually taking the moniker Partido Revolucionario Institucional, or the Institutional Revolutionary Party (PRI). The PRI effectively became Mexico's "state party," dominating both federal and local elections and capturing every presidential election, increasingly through fraud and corruption, until Vicente Fox of the National Action Party (PAN) won the 2000 presidential election. Although the PRI no longer dominates Mexican political office, it remains one of the three major party contenders, along with the PAN, seen as more free market oriented, and the Party of the Democratic Revolution (PRD), positioned to the left of the PRI.

The Mexican Constitution provides for the President to be elected through direct popular vote with only a plurality of votes cast. This type of first-past-the-post system normally gives majorities in two-candidate races or those in which third party candidates have little support. With three major political parties, however, majorities become far less likely, and plurality winners may actually lose a huge majority of the popular vote and take office only because of a divided majority. The three presidential elections held since the widely-acknowledged freeing of the ballot box in the mid-1990s all resulted in only a plurality win for each of the victors, and a successively smaller plurality at that, as the Mexican party system gradually evolved from the clientelistic control of the PRI to a viable three-party system.

The Clash of '06

The presidential election of 2006 proved the susceptibility of the plurality-win system to fraud in such a narrow race, and to popular discontent when the winning candidate lacks support from a large majority. Initial results showed a highly contested race between PAN candidate Felipe Calderón and PRD candidate Andrés Manuel López Obrador, with PRI candidate Roberto Madrazo taking a somewhat distant third.

The close preliminary results triggered an automatic recount, in which Calderón bested López Obrador by 243,934 votes, just 0.58 percent of the total. Calderón's winning percentage, however, fell barely higher than one-third all votes, at 35.89 percent. Viewed another way, a full 64.11 percent of votes were not cast for Mr. Calderón, but for the other two major party candidates, numerous smaller party candidates, independents, write-ins, and in blank ballot protest votes.

A winning plurality for Mr. Calderón meant that only 35.89 percent of voters, only slightly more than one-third, felt properly represented, while as many as 64.11 percent did not receive proper presidential representation for the next six years. Since democratic practice insists on a majority of popular support with respect to the rights of political and social minorities, an administration lacking majority support at the outset also lacks a moral right to govern, set agendas, and implement policies.

Mr. Calderón's time in office has seen great social and political instability in Mexico. It is likely that his administration's policies do not adequately reflect the wishes of a majority of Mexicans who supported other candidates in 2006. The same can be said for previous presidents who won with less than majority support in past elections, and for future presidents who continue to be elected under this outmoded system.

Unresolved Issues: The 2012 Election

The 2012 presidential election in Mexico will be held on July 1 and pits the three major-party candidates against one another: Enrique Peña Nieto of the PRI, Andrés Manuel López Obrador again of the PRD, and Josefina Vázquez Mota of the ruling PAN. Mr. Peña Nieto has led most polling since November 2011, followed by 2006 near-winner Mr. López Obrador and Ms. Vázquez Mota battling for second place.

Student protests in May against Mr. Peña Nieto as the candidate of the once-dominant PRI, however, have effectively boosted Mr. López Obrador's poll numbers and place him in closer contention with Mr. Peña Nieto. The student protests also had the effect of launching the second presidential debate, held on June 10, onto major broadcast television and a national audience. As all candidates come under increased scrutiny, polling is likely to again fluctuate. If no candidate ends up securing a majority of the popular vote on July 1, however, Mexico will again find itself led, perhaps controversially, by the winner of the simple plurality, and again discounting the wishes of the majority of Mexican voters.

A Majoritarian Fix

FairVote advocates a reform that both ensures winning candidates receive majority support even in the face of multiple candidacies and gives value to individual voter choice. Most presidential elections around the world rely on two-round runoff elections, as discussed in FairVote's 2006 report on presidential elections around the world. 

Used to elect Ireland's president, Instant Runoff Voting provides for more efficient and more representative elections than does plurality voting and even two-round voting, as discussed by Erin Ellis in her blogpost on the Egyptian presidential elections.

Advocated by FairVote's Rob Richie for elections in North America by an Election Law Journal article in 2004, IRV allows voters to rank the candidates in a race, putting "1" by the candidate they prefer the most, a "2" for the candidate they prefer next, and so on, until all candidates receive a rank. After tallying all voters' first-ranked choices, the candidate who receives the lowest level of support is eliminated. The second-ranked choices of voters who selected the now-eliminated candidate as their first choice are then added to the totals of the remaining candidates. This process is repeated until only two candidates remain and one of them receives an outright majority.

You can read more about FairVote's ideas about Instant Runoff Voting here.