By Daniel Lak
BBC News, Mexico
The internal conflicts of democracy were highlighted in Mexico this week as a free election - only the second in Mexican history - produced a historic result but left the country bitterly divided on political lines.
Now is the time to unite Mexico: Felipe Calderon
The candidate from the governing National Action Party, Felipe Calderon, won the presidency by the closest of margins - around 220,000 votes of 41 million cast last Sunday.
He has been declared the official winner by the Federal Electoral Institute, which now hands the result over to a seven-judge tribunal empowered to handle any challenges.
Mexican presidential elections are first past the post so theoretically the margin of victory does not matter.
But Mr Calderon's centre-left opponent, Andres Manuel Lopez Obrador of the Party of Democratic Revolution, said he would not accept the close result and wanted a full recount of all the votes.
"We are going to the Federal Electoral Tribunal with the same demand - that the votes be counted - because we cannot accept these results," he told a sombre group of supporters in Mexico city.
"We are always going to act in a responsible manner, but at the same time, we have to defend the citizens' will."
Mr Calderon knew he was winning from the early stages of the more than 30-hour long official tally.
Speaking well before counting was due to end, he called on Mr Lopez Obrador to concede his victory and to join him in a national unity cabinet.
"Now is the time to unite for Mexico," he said, in an offer certain to be spurned for at least as long it takes for Mr Lopez Obrador to exhaust his options to overturn the result.
As expected, the 55-year-old populist former mayor of Mexico City appealed to his supporters to take to the streets and join him for a rally against the election result on Saturday afternoon.
In the closing days of the campaign last week, more than half a million people listened to Mr Lopez Obrador's last speech before balloting began. He inspires an almost fanatical devotion among his followers.
Lopez Obrador inspires fanatical devotion among supporters
Many of those people are from Mexico's poor and working classes and there seems to be a widespread belief among them that the election was stolen by Mr Calderon's ruling party.
"It's 1988 all over again," said taco seller Ramon Fernandez, standing in a shopping precinct of the capital, surrounded by middle-class supporters of Mr Calderon.
That is a reference to an election 18 years ago when a substantial lead by the leftist candidate, Cuauhtemoc Cardenas, disappeared during what was described as a "computer crash" by election authorities.
The candidate of the PRI - the Institutional Revolutionary party that dominated Mexican politics from 1929 until 2000 - won by a narrow margin.
In this election, held for the second time under newly-designed rules to eliminate the vote rigging and fraud of the past, the challenges to the result can go on until September, and a president must be sworn-in in early December.
In the coming weeks, legal proceedings and street protests will create uncertainty and perhaps unrest.
Mexican politics is deeply divided. But political scientist Dr Eric Magar Meurs, of the Technology Institute of Mexico, says he doubts that Mr Lopez Obrador wants to force his way into power.
"He has to make his point, he has to show his supporters that he takes their concerns about this election seriously but if he gets a recount and he still loses than I think he'll step aside. That's the crucial moment for the system," he said.
"No one's talking about violent revolution here, or so we hope."