These problems have led most prognosticators to predict gains for the center-left Partido Revolucionario Institucional (PRI) along with losses from the governing center-right Partido Acción Nacional (PAN). The socialist Partido Revolucionario Democrático (PRD) – associated with the unpopular leadership of the controversial Andrés Manuel López Obrador – is expected to lose ground as well. Though López Obrador very nearly won the presidency in 2006; his ungracious post-election behavior has alienated many voters from the PRD. The 'voto nulo' movement's success may be partly due to the PRD's fall from grace; the major alternative is now the PRI, which ruled Mexico in an increasingly heavy-handed and corrupt fashion for 71 years until voters cast the party out of the presidency and into the wilderness in 2000. Thus, the contest is between different flavors of the establishment, leading to voter disenchantment and resentment.
A final explanation for the success of 'voto nulo' can be derived from a quirk in the electoral system. In most MMP systems, balloting entails two votes; one for a constituency candidate, the other for a party; constituency seats are decided by plurality rules, the top-up seats are then allocated to ensure that each party has roughly the same percentage of seats as votes. Conversely, the Mexican system allows only one vote, for a constituency candidate. These votes do double duty, based on the affiliation of a given constituency candidate, they also count as party votes. According to a study by Professors Clemente Quinones and Richard Vengroff of the University of Connecticut, this unorthodox method was implemented in the 1980s by the PRI, which hoped it would decrease sincere voting and allow the party to remain in office. However – to briefly summarize – the study concludes that most voters adapted to the system after a period of strategic voting, and largely returned to casting sincere ballots by the 2000 election (when the PRI lost power). Mexico's democracy is still learning to walk upright as it were, the long period of PRI domination only receded 9 years ago. It seems that voters are upset less with their system of voting than with the national political culture. However, Mexico has developed into an impressively open and pluralistic polity in a short period of time; those considering the arguments of the 'voto nulo' movement should keep in mind that the Mexican MPP system ensures that diverse views will be represented; for those who cast valid ballots, that is.