Even when he was a long shot, conservative Felipe Calderon promised to reach out to rival political parties and build a coalition government the likes of which Mexico has never seen.

Now the 43-year-old former energy secretary and apparent winner of the closest presidential race in the country's history may have to make good on that promise as he faces the monumental task of bringing together a divided nation and building a government that can get things done.

"Only a coalition government can provide the consensus, the dialogue and the inclusive proposals necessary to move the country forward," said Arturo Sarukhan, a key Calderon adviser. "Without it, very little will likely get accomplished."

It won't be easy to unify a Mexico so narrowly torn between Calderon and his main rival, former Mexico City Mayor Andres Manuel Lopez Obrador. Preliminary results show Calderon, of outgoing President Vicente Fox's National Action Party, with a mere 1 percentage point advantage.

The results were so close that the Federal Electoral Institute will reopen every ballot box starting Wednesday, double-checking vote counts for what it hopes will produce an undisputed winner.

Some Lopez Obrador supporters are already crying fraud, although fears of violence that many believed would accompany a close race haven't materialized.

As far back as July 2005 _ when he was a third-place contender for National Action's presidential nomination _ Calderon said that as president he would seek consensus and reach across party lines in forming his government.

On Monday, he asked the country to move past what was an exceptionally nasty campaign.

"Mexico's future requires unity among all of us that can rise above the political contrasts of the presidential campaign," Calderon said. "It's time to begin a new era of national reconciliation."

But coalition-building is relatively new territory for Mexico. For more than seven decades the Institutional Revolutionary Party, or PRI, was the only game in town _ controlling the presidency from 1929 until Fox's historic victory in 2000.

It held power by appealing to unions, business leaders and anyone else who would support it. When that didn't work, vote-buying or outright fraud often did. Opposition parties didn't really gain ground until near the end of the PRI rule, especially after a disputed 1988 presidential election.

The PRI, whose presidential candidate finished a distant third on Sunday, could hold the key to a coalition government, since no party will control a majority in Congress.

Calderon could reach out to the PRI by naming some of its members to his Cabinet. But with the party still reeling from its bad showing, the PRI might not hold together as a solid voting bloc _ meaning Calderon's best shot at constructing a unified government might entail striking deals with Lopez Obrador's Democratic Revolution Party, or PRD.

Sarukhan said the Calderon campaign has been "keeping channels of communication open" with the PRD and the PRI, but no formal negotiations for Cabinet posts will begin until a final vote count is released.

"The understanding is going to be, 'You sit in the Cabinet, or somebody from your party does, and you deliver the votes necessary to move key reforms through Congress,"' Sarukhan said. "It is positions for votes."

Consensus-building takes more than a diversified Cabinet, however. Fox's administration was stocked with PRI leaders and leading leftists _ and still made little headway with Congress.

What's more, Calderon's track record for negotiating with political opponents is less than stellar. During his tenure as head of National Action's voting bloc in the lower House for the first three years of the Fox administration, nearly all of the president's central reforms were defeated.

And some say the negative campaign ads that helped Calderon catch Lopez Obrador after trailing for most of the race might now make consensus-building tough.

Said Michael Lettieri of the Washington-based Council on Hemispheric Affairs: "After putting horns and a tail on your opponent and calling him the devil, do you think he will really want to sit down at the table?"