Mexico's historic protest.

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 for a month. When the farmers returned to Tabasco empty-handed, they were attacked by PRI mobs on the streets of Villahermosa.

Undeterred by the repression, in 1996, AMLO led Chontal Indian farmers in a blockade of sixty drilling platforms to protest the contamination of their communities by PEMEX, the nationalized oil corporation. Troops and police beat Lopez Obrador, jailed him, and broke up the blockade on orders of Governor Madrazo and President Ernesto Zedillo.

But Lopez Obrador proved indefatigable. Months later, he led a people's referendum condemning a Zedillo government plot to dump billions of dollars of bank debt upon the backs of Mexican taxpayers so that the banks could be sold to U.S. and Spanish investors.

As president of the PRD, Lopez Obrador engineered the victory of his one-time mentor Cuauhtemoc Cardenas as Mexico City's first elected mayor. Three years later, he himself won the post on the same day in July 2000 that Vicente Fox became the first opposition president of Mexico.

AMLO has proven to be an extraordinarily popular mayor who builds massive public works, provides free medical attention for all underclass residents, and offers a $60 monthly pension to every uncovered senior citizen within the city limits. Pugnaciously committed to his ethos of "Los Pobres Primero!" ("The Poor First!"), Lopez Obrador is relentlessly assailed by Fox and his neoliberal cronies as a dangerous populist.

From the other side of the political spectrum, Subcomandante Marcos of the rebel Zapatistas said AMLO represented "the left hand of the right." Marcos criticized AMLO for surrounding himself with "Salinistas" (former associates of the now-reviled ex-president Carlos Salinas). And Marcos excoriated AMLO for shutting down the investigation into the death of human rights lawyer Digna Ochoa. Nevertheless, the Zapatistas stood resolutely against AMLO's ouster, saying it was designed to "annihilate the electoral option by which free men and women can come peacefully to power."

Despite the government onslaught, AMLO's popularity kept rising. In March polls, he stood 13 points ahead of the probable PAN candidate for president, Interior Minister Santiago Creel. At this point in the race, AMLO, who is stepping down as mayor to concentrate on his run for president, seems all but invincible. That is, if he is not removed from the competition by hook or by crook.

The initial effort to oust him from the race has now backfired. On red alert after the PAN was soundly trounced in 2003 midterm elections, Fox, Creel, and Attorney General Rafael Macedo de la Concha (a real general) cooked up a plot to keep AMLO off the 2006 ballot. During Christmas week 2004, Mariano Azuela, the president of Mexico's Supreme Court, was summoned to Los Pinos, the Mexican White House, to iron out the legal wrinkles in the conspiracy.

They decided to go after AMLO for signing off on building an access road to a newly relocated hospital in the red-hot Santa Fe enclave in western Mexico City, where many transnational corporations are now headquartered. The owners of the expropriated slice of right-of-way, less than sixty yards long, obtained a court order to force the city to cease and desist, with which Lopez Obrador promptly complied. But the promoters then complained that heavy equipment parked near the abandoned construction was blocking their access and won a contempt of court citation against AMLO.

Fox and the PRI seized on this puny issue as a way to do AMLO in. On April 7, the PRI-PAN majority in the lower house of Congress voted to strip Lopez Obrador of his immunity from prosecution, which elected officials traditionally have. The desafuero (outrage) would have removed him from office, laid him open to prosecution and a possible jail term of one to eight years, and prohibited him from running for office.

In classic AMLO mode, he vowed to run his presidential campaign from a prison cell, much as Francisco Madero had back in 1910 after the dictator Porfirio Diaz clapped him in jail. (Denied victory, Madero proclaimed the Mexican revolution. History is one of AMLO's keenest weapons.) AMLO summoned the masses, a sometimes-dangerous proposition in a nation where the bad gas of class and race hatred seeps just below the stoic surface of society. On Desafuero Day, April 7, 330,000 people turned out to accompany their beloved leader. It was the largest political outpouring in the capital in the seventeen years since Cardenas was robbed of the presidency. Despite dire warnings, the gathering was a peaceful one, some would say too peaceful.

Now, on April 24, the crowd had tripled. From early dawn, the civil society reassembled itself by the Museum of Anthropology in whose vaults the history of Mexico reposes. Out in the park, old people, young people, straight people, gay people, city people, country people, political people, just people people, but mostly brown people, the people the Zapatistas' Marcos calls "the people who are the color of the earth," gathered to express their outrage. Their mouths covered with white tapabocas (surgical masks) and their shoes slapping at the pavement, the people moved in silence along the route of the murdered students. Overhead, federal police helicopters buzzed and spooked the marchers, since it had been a signal from a government helicopter that had triggered the massacre at Tlatelolco. My companero de marcha, Humberto Trujillo, a cagey old farmers' lawyer and a veteran of '68, glanced up in alarm over the top of his tapaboca.

With their fists pumping silently into the broiling noon, the marchers' silence lent them an aura of moral authority. They carried hand-lettered poster board: "They Will Not Listen to Our Words--Now They Must Listen to Our Silence," "We Are No Longer Invisible Citizens," "Todos Somos El Peje" ("We Are All El Peje," adapting a slogan once exclusively reserved for Subcomandante Marcos), and "I Voted for Fox and I Repent!"

Under the column of the Angel of Independence on the Avenida Reforma, four men unfurled a mammoth banner that read: "Revolution Every 100 Years: 1810 [liberation from Spain], 1910 [the revolution], 2010 ???"

"This is not just about one person anymore," said Nuri Fernandez, a longtime political activist. "It belongs to all of us now!"

Inside the teeming Zocalo, Lopez Obrador spoke from a stage erected directly in front of the National Palace, the seat of government he could be inhabiting next year. He declared his populist views, standing against the privatization of PEMEX and the electricity industry and against the unbridled free market. "We must not allow ourselves to become victims of globalization but we must learn how to manipulate it for our own benefit." If elected president, he vowed not to engage in a witch-hunt of his opponents. And above all, he vowed, "Los Pobres Primero!"

Three days after the unprecedented March of Silence, Vicente Fox took to national television to announce he accepted the resignations of Attorney General Macedo and his bulldog prosecutor, Carlos Vega Memije. The charges against AMLO would be consigned to legal limbo. The president promised to send legislation to congress that would modify Mexico's legal proceedings and guarantee a presumption of innocence. Shortly thereafter, the government said it would no longer prosecute him.

Everywhere he goes these days, AMLOs lucha has gathered momentum. Troupes of street venders follow the marches, hawking buttons and T-shirts that bear his name, as well as compact discs of "The Cumbia [The Dance] of El Peje."

Andres Manuel Lopez Obrador is riding the pendulum swing that is moving across Latin America. The neoliberal model savaged the poor, depleted national economies, drove the farmers off the land, and made consumers dependent on products made by far off multinationals. All over Latin America today, the people are on the march, and they are demanding leaders who respond to their needs, not those of Washington or the International Monetary Fund.

For millions of Mexicans, AMLO is just such a leader.

If he can survive the tradition of assassination--which dates back to Madero and Zapata and most recently revealed itself in the 1994 hit on PRI presidential hopeful Luis Donaldo Colosio--Mexico may soon have a leader who puts the poorest first.

Longtime Mexico hand John Ross's latest book is. "Murdered by Capitalism: A Memoir of 150 Years of Life & Death on the U.S. Left."