Enrique Peña Nieto, who polls show is the favorite to win Mexico's July 2012 presidential election, is defending himself after becoming the butt of jokes for being unable to identify the authors and titles of several books.

During a visit to the Guadalajara International Book Fair over the weekend, Peña Nieto, the only candidate of the Institutional Revolutionary Party, or PRI, got confused about certain authors and was unable to recall the titles of books he had listed as his favorites.

The politician said Enrique Krauze wrote "La silla del aguila," a work by Carlos Fuentes.

"There is another book by him (Krauze) about strongmen. I don't remember the exact title, it was a book I liked," Peña Nieto said.

"I have a hard time recalling the titles of books," the politician said, adding that the Bible was another work that had made an impression on him.

Peña Nieto's mistakes unleashed a wave of jokes on the Web and social-networking sites like Facebook and Twitter, where #LibreriaPenaNieto is one of the most followed feeds.

"I am reading the tweets about my mistake yesterday, some very critical, others funny even. I appreciate them all. Let's keep working for Mexico," Peña Nieto said in a Twitter posting on Monday.

Anyone could have made the same mistake, Peña Nieto said during an interview with Radio Formula.

Some politicians used his gaffe as an opportunity to criticize the former governor on Twitter.

Peña Nieto "believes the author of the Bible is John Paul II," Sen. Carlos Navarrete, of the leftist Party of the Democratic Revolution, or PRD, said in a Twitter posting.

"If ignorance hurt, Enrique Peña Nieto would be screaming," Labor Secretary Javier Lozano said.

"Enrique: the issue that concerns us is concrete. Your brutal ignorance offends and is a threat. I applaud you for giving yourself away so soon," Lozano said in his posting.

The matter picked up steam when Peña Nieto's eldest daughter, Paulina Peña, resent a Twitter message from her boyfriend that labeled her father's critics "a bunch of wimps" and "part of the underclass" that only criticizes "those they envy."

Peña Nieto apologized for his daughter's statements, saying on Twitter that hers "was an emotional reaction" over his gaffe at the book fair and was "an excessive" action.

Ernesto Cordero, who is vying for the nomination of the ruling National Action Party, or PAN, also criticized Peña Nieto, but then he got confused while responding in an interview to a question about Colombian writer Laura Restrepo, referring to her as Isabel.

The 45-year-old Peña Nieto, a former governor of Mexico state, has said he wants to promote ideas and compromise to win the backing of Mexicans.

The PRI, which governed Mexico from 1929 to 2000, is trying to regain the presidency after two straight losses.

Peña Nieto announced his bid for the PRI's presidential nomination on Sept. 20, a few days after ending his term as governor of Mexico state, which surrounds the Federal District and forms part of the Mexico City metropolitan area.

The former governor was given a clear path to the nomination in November, when Sen. Manlio Fabio Beltrones, the only other candidate vying to head the ticket in the 2012 elections, withdrew from the race.

Mexico will hold its presidential election on July 1, 2012, electing a successor to President Felipe Calderon of the PAN.

The leading candidates are Peña Nieto, who will be the standard-bearer of the Compromiso por Mexico coalition formed by the PRI, the Mexican Green Party, or PVEM, and the New Alliance Party, or PANAL; and former Mexico City Mayor Andres Manuel Lopez Obrador, who heads the ticket of the alliance formed by the leftist Party of the Democratic Revolution, or PRD, the Workers Party, or PT, and the Movimiento Ciudadano.

The PAN, which is going it alone in the election, has not decided on a candidate yet.

Josefina Vazquez Mota, Santiago Creel and Cordero are vying for the PAN's nomination.

Some 80 million Mexicans will be eligible to vote for a new president, 628 legislators and thousands of other officials in next year's general elections.