This Sunday, the citizens of the State of Mexico, the country’s most populous state, will elect a new governor. But Sunday’s election is more than just a state contest: it has the attention of the entire nation. The current governor, Enrique Peña Nieto of the Partido Revolucionario Institucional (PRI), is the clear frontrunner for the 2012 presidential election and this weekend’s contest is seen as a test for him and his party.

Every electoral poll published in the last three or four years has consistently noted the popularity of Peña Nieto. According to recent polls, if the elections were held today, the PRI would return to the presidency after 12 years of Partido Acción Nacional (PAN) governments. And this would happen by a wide margin.

And this election is the first battle for the presidency. If the PRI wins, the popularity of  Peña Nieto and his party would be validated. But it is also an opportunity for the PAN and Partido Revolucionario Democrático (PRD), to beat Peña Nieto and PRI or, at least, to weaken his position. Indications are that Sunday will be a PRI victory: polling suggests that Peña Nieto and the PRI will win with a clear advantage –more than 50 percent of the votes in the first round.

A victory would reinforce the PRI’s position as the strongest party in the country. It has won over significant governorships and some large cities or municipalities. What has made it so strong is being mostly united behind Enrique Peña’s presidential bid. In this sense they learned their lesson from the 2006 election where two main groups fought for the candidacy and ended up sending the PRI to third place.

This time we shouldn’t expect this to happen.

The PRD and PAN are a lot weaker than they were six years ago, when a tight election between the two parties created a tense situation after Felipe Calderón’s (PAN) presidential election. The PRD has to live with the very unpopular decision of Andrés Manuel López Obrador of not recognizing the official results and closing down Mexico City’s main avenue for about a month. For its part, the PAN has been weakened by the not so great economic results of this administration, the influenza outbreak, the 2008 financial downturn, and a significant reduction in tourism due to the violence of the so-called war on drugs. Furthermore, the party lacks leaders that can mount a serious challenge to Peña Nieto.

Last year, just four years after the PRD called President Calderón a spurious president, the PRD and PAN formed an alliance that for the first in the Calderón administration resulted in a significant opposition to the PRI. The PRD-PAN won the state governorships of Oaxaca, Puebla and Sinaloa—three PRI strongholds that had never faced a change in parties. But their strength was still questioned as the alliance’s candidates were all former PRI politicians.

With those victories in hand, the PAN and PRD leaderships tried to form an alliance to challenge the PRI’s candidate in the State of Mexico, and thereby diminish Peña Nieto’s political clout. But it wasn’t as easy this time. The state legislature passed a highly controversial reform to the state’s election laws to make it harder and more politically expensive to build the coalition. Peña Nieto also showed his political skill. Rather than choosing his closest collaborator or his cousin as the PRI candidate, he selected Eruviel Avila, a politically savvy politician.

If the polls are right, and the PRI wins by a clear margin on Sunday, the main loser will be the PAN. It will likely move to third place in national popularity.

Still, Mexicans will have to wait another six months to see whether Peña Nieto is still perceived as unbeatable, or whether a potential alliance between the PRD and PAN can pose a significant challenge.

*Pedro Velasco and Alberto Saracho are guest bloggers to AQ Online. Pedro is an associate researcher and Alberto is executive director of Fundación IDEA, one of Mexico’s first non-profit independent think-tanks.