Imagine the following. After a close race in 1960, Richard Nixon goes nuts, starts living in a tent with his followers in Washington, DC, and then travels around the country telling everyone he sees that John F. Kennedy is not the real president. Given that situation, do you think he'd have a chance to win again in 1964 or 1968?
That is essentially what the PRD is hoping for now, because the party nominated Andrés Manuel López Obrador as its presidential candidate for 2012.
The person who is likely the happiest with that outcome is the PRI's Enrique Peña Nieto, who now solidifies his position as favorite. We've got another year to go, so a lot can happen, but AMLO starts in a deep hole. There is a large chunk of the electorate that simply won't vote for him. A recent poll showed 35% of Mexicans had a negative or very negative view of him.