Gone are the days when Mexico’s first female presidential candidate, Josefina Vázquez Mota, could have transformed the presidential race with her historic candidacy with a high-profile break from the current leadership of her party, the ruling Partido Acción Nacional (PAN).

Over the past month, the man to watch in the Mexican presidential election — except, of course, for the longtime frontrunner Enrique Peña Nieto, candidate of the Partido Revolucionario Institucional (PRI) — has increasingly been Andrés Manuel López Obrador, the leftist candidate of the Partido de la Revolución Democrática (PRD), who previously served as head of government of the Distrito Federal from 2000 to 2005 and who narrowly lost the 2006 presidential race to current PAN president Felipe Calderón.

López Obrador led the 2006 polls throughout much of the campaign, much as Peña Nieto has led polls in the current presidential campaign, but narrowly lost after the PAN and the PRI launched negative attacks claiming that López Obrador would take Mexico down a path similar to that of Hugo Chávez in Venezuela.  Although those fears were overblown, they were strong enough to deny López Obrador a long-anticipated win.

Once regarded as a hopeless retread in the current campaign, López Obrador — or AMLO, as he’s also known in Mexico — has overtaken Vázquez Mota in polls for second place in the increasingly bleak race to become the main challenger to Peña Nieto.  Despite his narrow 2006 finish, López Obrador alienated much of the Mexican electorate by loudly protesting the vote result for months afterwards, a tactical mistake from which he never quite recovered.

So it was surprising, to say the least, when López Obrador placed just four percentage points behind Peña Nieto in a Reforma poll last week.  Other, more reliable polls, show Peña Nieto with a steadier lead — Peña Nieto has led every presidential poll since last year — but also show an unmistakable rise in support for López Obrador.  In one recent poll, he is even leading among independents and among college-educated Mexicans.

Rivals have taken notice — both the PRI and the PAN have taken aim at López Obrador in recent days. 

One sure boost for López Obrador has been the #YoSoy132 youth movement in Mexico — “I am 132” refers to the 131 students at Mexico City’s Ibero University who launched a protest against Peña Nieto’s candidacy.  A Peña Nieto win would return to power the PRI, which ruled Mexico with an autocratic bent for much of the 20th century.  Although the PRI lost the presidency in 2000 and 2006, it has remained one of Mexico’s three major parties, and it has won the largest share of seats in the Cámara de Diputados from 2003 to 2006 and since 2009. Since 2000’s breakthrough, when the PAN’s Vicente Fox won the Mexican presidency, no party has held 250-plus seats required to hold a majority in the Chamber of Deputies.

Legislative elections will be held on July 1 simultaneously with the presidential election.  The PRI, which currently controls 241 seats, is expected to return as the largest party if Peña Nieto wins, perhaps even with an outright majority.  The return of the PRI to control both the Mexican executive and legislature has, not unpredictably, spawned a strong response from both right and left.

With Mexicans weary after 12 years of a PAN-controlled presidency, and exhausted in particular by the Calderón administration’s long and bloody war against Mexican drug violence, a Mexican economy still recovering from the global financial crisis of 2008 and the inability of the PAN to pass tax and regulatory reforms through the Mexican Congress (where the PRI has blocked nearly all of the key initiatives of the Fox and Calderón administrations), López Obrador has been well-placed to capture the support of voters who want a change but who are also hesitant to return the PRI to power.

Fox — to the protests of PAN candidate Vázquez Mota — said last weekend that it was a farce that a PRI win would take Mexico back to its authoritarian past.  Fox has also admitted during that campaign that Peña Nieto has a virtual lock on the race, again to the dismay of his PAN colleagues.

While Fox has been undermining the PAN’s campaign, the founder of the PRD, Cuauhtémoc Cárdenas, was giving his very public support to AMLO and encouraging the sometimes unruly PRD to unite behind his candidacy.  Cárdenas, son of one of the most popular presidents in Mexico’s history, is widely seen as having won the 1988 presidential election, but was denied the presidency through fraud perpetrated by the PRI.