Andres Manuel Lopez Obrador called on a huge crowd of supporters to keep protesting while he pursues a legal challenge of Mexico's disputed presidential vote count, and to help him prevent "a backward step for democracy."
The fiery, silver-haired leftist said he would begin presenting his allegations to the nation's electoral court on Sunday, requesting that all 41 million votes cast be recounted to expose fraud he believes cost him the election.
"We are going to ask that they clean up the elections. We are going to ask that they count all the votes, vote-by-vote, poll-by-poll," Lopez Obrador said, calling on the army to protect the integrity of every ballot box.
He also called for marches nationwide, beginning Wednesday and converging on Mexico City for another rally on Sunday July 16.
And he provoked groans of disappointment from the packed crowd in Mexico City's central plaza when he told them not to block highways.
"This has been and goes on being a peaceful movement," he said. "We are not going to fall for any provocations."
The likelihood of continuing demonstrations suggests just how difficult it will be for the ruling party's Felipe Calderon to unify Mexicans, many of whom believe the nation has yet to overcome the decades of institutional corruption and fraud that kept its leaders in power.
Lopez Obrador took direct aim at President Vicente Fox, accusing him of conspiring with Mexico's autonomous elections agency, known as IFE, to engineer a victory for the ruling party's Calderon.
Lopez Obrador said Fox had betrayed the Mexicans whose outrage over repeated election fraud swept him into power in 2000 after 71 years of single-party rule by the Institutional Revolutionary Party, or PRI.
"He dedicated himself to attacking us and ended up being a complete traitor of democracy," Lopez Obrador said. "And if that weren't enough, the IFE, which should act with imparciality, turned into the pawn of the party of the right."
Lopez Obrador claimed earlier Saturday that there were more irregularities in last Sunday's balloting than under the PRI.
Election monitors from the European Union said they found no irregularities in the count.
Legal challenges were built into Mexico's elections process in recent years to help ensure clean elections, so Calderon can't be declared president-elect until the electoral court weighs allegations of fraud or unfair campaign practices. The court has until Sept. 6 to declare a winner.
The stakes are high as Calderon and Lopez Obrador appeal to the court of public opinion.
Lopez Obrador remains convinced he won the elections. He has millions of extremely devoted followers who believe only he can help Mexico's poor and downtrodden, and he views street protests as an effective means of pressuring the government and the courts.
Election officials say Calderon, of Fox's National Action Party, beat Lopez Obrador by less than 244,000 votes out of 41 million ballots -- or a margin of about 0.6 percent.
Calderon says the vote was clean and has taken congratulatory phone calls from U.S. President George W. Bush and the leaders of Canada, Spain and Colombia, among others, despite Lopez Obrador's plea for foreign governments to hold off on recognizing the result.
The crowd in the Zocalo Saturday night would accept nothing less than victory for the silver-haired former Mexico City mayor.
"We are never going to recognize this man (Calderon)," said Apolinario Fernandez, 37, a teacher from Lopez Obrador's home state of Tabasco in the southeast. "If he wants, let him govern in the north for the rich, but not in the south."
Calderon's strength is in Mexico's industrialized north while most of Lopez Obrador's supporters come from Mexico City and poor southern states. Many traveled all night to arrive at the demonstration, joining a sea of yellow, the color of Lopez Obrador's Democratic Revolution Party.
"We are ready to do whatever is necessary," said Belasario Cruz, 32, a farmer from Tabasco. "We are tired of the rich having everything and the poor having nothing."
There were no immediate reports of arrests or violence at the protests.
Political analyst Oscar Aguilar predicted that Lopez Obrador will never concede defeat.
"Once the election results are certified, he will open a permanent campaign of criticizing the government," Aguilar said.
Lopez Obrador claims a manual recount would confirm that hundreds of thousands of votes for him remain uncounted, miscounted or voided. The law allows such a recount only for specific polling places where credible evidence of irregularities exist. The leftist's supporters say that applies to at least 50,000 of the approximately 130,000 polling places.
If Lopez Obrador appears too radical, he risks hurting his party and its chances in the next presidential elections in 2012. If he appears too moderate, he risks disappointing his core supporters.
"His political stock would increase greatly for 2012" if he can concede defeat gracefully, Aguilar said.