presidential candidate Oscar Ivan Zuluaga, left, points as he faces Colombia's President Juan Manuel Santos during a televised debate in Bogota, Colombia.
Colombians vote Sunday in the nation's tightest presidential contest in two decades, an election that President Juan Manuel Santos deems a referendum on peace talks to end the Western Hemisphere's longest-running conflict.
His right-wing rival, Oscar Ivan Zuluaga, has challenged the slow-going negotiations with rebels in Cuba, accusing Santos of selling out to an insurgency that is already on the ropes.
Zuluaga is the hand-picked candidate of former two-term President Alvaro Uribe, who has played a major role what has been Colombia's dirtiest campaign in years.
A former Uribe finance minister who stresses his provincial roots as a contrast to Santos' blue-blood lineage, the 55-year-old Zuluaga won the most votes in a five-candidate field in the election's May 25 first round.
The last Invamer-Gallup poll gave Zuluaga a slim 48.5 percent to 47.7 percent lead over Santos, with 3.7 percent of respondents saying they would choose neither. Its margin for error was 3 percentage points.
The challenger has capitalized on widespread distrust for the rebel Revolutionary Armed Forces of Colombia, or FARC, and has set what seem to be impossible conditions for continuing the peace talks launched 18 months ago in Havana.
The insurgents must halt all military activity, says Zuluaga, with some essentially having to agree to jail time. He and Uribe accuse Santos of offering impunity to the rebels, who have killed and kidnapped for five decades, sown anti-personnel mines and forcibly recruited minors.
Santos, 62, denies he would let war criminals to go unpunished. And he is certainly no dove. As Uribe's defense minister and then president, he wielded Colombia's U.S.-backed military to badly weaken the FARC, including killing its top three leaders.
The bulk of Colombia's left has endorsed Santos as, says political scientist Arlene Tickner of Universidad de los Andes, he steered the nation to "a historic juncture at which the possibility of putting a peaceful end to the conflict needs to be seized."
Santos won important endorsements last week and may have regained some momentum. He got the backing of 80 top business leaders and announced exploratory talks with the National Liberation Army, Colombia's other, far smaller rebel band.
Yet the U.S.-educated incumbent has a "severe likeability and trust problem," says analyst Adam Isacson of the Washington Office on Latin America, and has been "unable to shake the image of an out-of-touch Bogota aristocrat who will promise everything and deliver little."
Santos is opposed by Colombia's cattle ranchers and palm oil plantation owners, beneficiaries of a deal Uribe made with far-right paramilitaries that dismantled their militias. Large landholders had by then consolidated control over territory that the militias had largely rid of rebels while driving at least 3 million poor Colombians off the lands. They dislike Santos' peace process.
The slow pace of talks has not helped Santos. Framework agreements have been reached on agrarian reform, dismantling the illegal drug trade and a rebel role in national politics.
But analysts say Santos could have done much better at communicating the gains and building public support.
The peace process also ranks relatively low on most Colombians' list of priorities. The Gallup poll found less than 5 percent of respondents to believe the FARC will be the next president's main problem. Spreading the benefits of a growing economy is more important to many.
Economic growth averaged 4.5 percent annually during Santos' four years and 2.5 million jobs were added. But analysts say the president has done little to improve education, health care and infrastructure.
Less important, apparently, to supporters of Zuluaga and Uribe are the multiple scandals of the latter's presidency.
They include extra-judicial killings of innocent civilians to boost military body counts, illegal spying on judges and journalists and the funneling of agricultural subsidies to well-heeled ranchers. Uribe won a Senate seat in March after being constitutionally barred from another presidential run.
The campaign's mud-slinging, meanwhile, has been fierce. In its final days, the Zuluaga camp accused Santos' campaign of a vote-buying push on the Caribbean coast "without precedent in Colombia."