Mexico's election system is unique in Latin America. Despite its independent electoral tribunal, professionalized election administration and partly proportional legislature, the president is elected by plurality. The norm is a two-round system whereby the winner must have a majority and, if he or she does not, the top two candidates compete alone in a second round.

Americans are well aware of the problems that stem from close plurality elections. 2000's race came down to a few precincts in a few counties in a single state. Concerned voters blamed ballot design - even fraud - for the eventual outcome. 2004 further eroded confidence in our democracy infrastructure as a tight race for Ohio's decisive electoral votes raised concern about partisan election administration and allegedly fraudulent Diebold voting machines. Some Mexicans feel the same way now that all ballots have been counted following their elections on July 2.

In a race that could decide Mexico's economic fate, conservative Felipe Calderon, championing free trade and North American integration, faced off against left-wing populist Andres Manuel Lopez Obrador. Both came in with just around 36% of votes each - nowhere near a majority - and Calderon edged Obrador by less than 0.6% of valid votes. Commentators called it Mexico's most negative campaign to date, with tactics deliberately imported from one of the free world's last remaining plurality systems:

TomPaine.com:

Coached by Morris" ilk, AMLO"s rivals, Felipe Calderón Hinojosa of the right-wing Partido Acción Nacional (the party of current president Vicente Fox) and Roberto Madrazo Pintado of the long-ruling Institutional Revolutionary Party (PRI), produced a barrage of negative ads in recent months. The U.S.-style mudslinging set a new standard in Mexican politics.

Unsurprisingly, Obrador will challenge the result.

Few are talking about the 21.5% of voters who supported moderate left candidate Roberto Madrazo Pintado. If there were a runoff round, most of that support would break in favor of one or the other leading candidates. Under instant runoff, Obrador and Calderon, needing a majority, would have campaigned more gently for the second choices of Madrazo supporters.

[ More on IRV ] [ FairVote's report: Majority Rule in International Presidential Elections ]

More to come on the results of Mexico's Congressional election, run under a mixed-member system of part proportional voting, part winner-take-all districts. There the outcome was far more balanced with seats going to all three major parties. Because Mexico's president is directly accountable to voters, not the confidence of the majority coalition, the "divided" legislature should result in public policies more even than presidential campaign rhetoric would have let on.