"[It] suddenly seems like the inevitability of his [Pena Nieto's] election is not so clear and without a doubt, the role of the students has been an important factor ... because it's been spontaneous, it's not been controlled by other parties, it's viewed as an expression of general public sentiment against a conglomerate of a news media."

- Eric Olson from the Mexico Institute at the Woodrow Wilson Center

Pena Nieto has benefited from widespread discontent over the way President Felipe Calderon's National Action Party (PAN) has governed Mexico, with their candidate, Josefina Vazquez Mota, floundering in the polls.

But thousands took to the streets on Sunday in protests against Pena Nieto organised by the student-led 'I am 132' movement. They oppose a return to power of his Institutional Revolutionary Party (PRI), whose 71-year rule of the country up until 2000 was marred by corruption and authoritarianism.

Pena Nieto has also been damaged by allegations that the country's main broadcaster, Televisa, had colluded with his party to favour his candidacy.

It is the candidate of the left, Andres Manuel Lopez Obrador of the Party of the Democratic Revolution (PRD), who narrowly lost out to Calderon in 2006, who could benefit from any backlash against Pena Nieto.

In recent weeks, Lopez Obrador has been gaining ground in the polls.

But whoever wins this election will have to grapple with a country ravaged by drug violence and poverty.