Mexico's historic protest.

• Author: Ross, John

There are moments here when civil society comes out of its house and fills the streets with righteous indignation, the heat of human bodies fusing into one great fist of frustration. Such moments are rare in Mexico and to be savored: the marches of the doomed students in 1968; the fury that followed the stealing of the 1988 presidential election from Cuauhtemoc Cardenas; the repeated mobilizations in solidarity with the Zapatistas that have filled the Zocalo plaza to the brim.

Sunday, April 24, was such an outpouring. Police estimated that 1.2 million citizens took to the streets of Mexico City, this ancient Aztec capital. This was the largest protest in Mexican history, and they were defending the capital's leftwing mayor, Andres Manuel Lopez Obrador (commonly referred to by his initials, AMLO, or his nickname, "El Peje," a gar-like fish from his native Tabasco state). His opponents were trying to oust him from office, toss him in the pokey, and bar him from next year's presidential ballot. Since the 2003 "mid-term elections, AMLO has been running ten to twenty points ahead of President Vicente Fox's rightist PAN party and the long-ruling PRI, which Fox displaced from the presidency in 2000.

In a country that is overwhelmingly Catholic, the April 24 gathering here drew bigger numbers than even the coronation of a new Pope, which took place on the same morning in faraway Rome.

Under scorching skies, the multitudes converged on Chapultepec Park for the nine-kilometer hike to the Zocalo. The route was purposefully the same as taken by striking students in September 1968, just a month before hundreds would be massacred by army troops downtown. Like that historic mobilization, today's march would be a silent one.

Lopez Obrador made his bones in the swamps of Tabasco, a sweltering oil-rich entity that is a kind of Mexican Louisiana. Twice Lopez Obrador and the leftist Party of the Democratic Revolution (PRD) tried to wrest the governorship from the PRI, and twice they were swindled out of victory, once when the PRI engaged in a vote-counting fraud and once when the PRI vastly exceeded the state campaign limits.

After kingfish Governor Roberto Madrazo, now president of the PRI and its likely candidate for the presidency, stole the 1994 contest with a billion pesos provided by a fugitive tycoon who had just looted two newly privatized banks, AMLO marched hundreds of ragtag campesinos 1,000 miles up to Mexico City. There they encamped in the Zocalo...