MEXICO DF -- When Mexican President Enrique Pena Nieto arrived at the March 18 rally, he was greeted like a rock star. Hundreds of local residents and employees of Petroleos Mexicanos had gathered in the eastern state of Veracruz for the annual celebration of the 1938 expropriation of foreign wells and the founding of Pemex. The workers, all dressed in white shirts and guayaberas bearing the Pemex logo, leaned over waist-high barriers to try to touch the photogenic president. They cheered and sang, breaking frequently into a chant normally reserved for the national soccer team. An outsider would have never guessed that, just three months earlier, Pena Nieto, had signed into law a constitutional amendment that Pemex, its powerful union and its political backers had fought against for decades.