Enrique Pena Nieto of the Revolutionary Institutional Party held a significant lead for president as voting was under way Sunday in Mexico's 31 states. His party controlled the Mexican presidency through much of the 20th century before losing the past two elections. (Associated Press)

Enrique Pena Nieto of the Revolutionary Institutional Party held a significant lead for president as voting was under way Sunday in Mexico's 31 states. His party controlled the Mexican presidency through much of the 20th century before losing the past two elections. (Associated Press)