Presidential candidates, left to right, Oscar Ivan Zuluaga, Enrique Penalosa, Colombia's President Juan Manuel Santos, Martha Lucia Ramirez and Clara Lopez are seen during a televised debate in Bogota May 23, 2014. Colombia's presidential elections will be held on May 25. (Fredy Builes/Reuters)

Colombians will vote for president Sunday, and only a master fabulist like the late Gabriel García Márquez might have imagined a contest so loaded with high-stakes political drama and shadowy intrigue.

Running for reelection is incumbent Juan Manuel Santos, a close U.S. ally who seemed to be cruising toward an easy win. His first term brought Colombia steady economic growth and groundbreaking peace negotiations with FARC guerrillas, taking the country further than ever toward ending its half-century civil war.

But in recent weeks, with accusations flying and scandalous muck raked across news headlines, former finance minister Óscar Iván Zuluaga has been surging in polls, turning the five-candidate race into a two-man grudge match.

The debate is not an ideological one. Both men are conservatives who would preserve Colombia’s close ties to the United States and further free-trade policies for Latin America’s third most populous country.

Instead, the race appears to be pivoting on two other, related factors: the controversial peace negotiations with the FARC and the abiding influence of ex-president Álvaro Uribe, now a senator, who remains the country’s most powerful and polarizing figure.

Santos is Uribe’s arch-rival. Zuluaga is Uribe’s handpicked protege.

“Voters see this as a battle between Santos and Uribe, not Santos and Zuluaga,” said a Javier Restrepo, a pollster with Ipsos, noting that Zuluaga was so unknown that more than half of Colombians had never heard him as recently as January.

But he has the still-popular Uribe behind him.

The latest surveys show both candidates winning about 28 percent of the vote Sunday, with the three others polling at 10 percent or less. If no candidate earns 50 percent, a runoff will be held June 15.

Polls also show Santos and Zuluaga drawing about equal amounts of support from urban and rural voters, regardless of sex or income. Less clear is how a spate of recent scandals will affect Sunday's outcome.

Santos appeared to suffer after claims surfaced that a Miami-based Venezuelan political consultant, Juan José Rendón (known as “Jota-Jota” for his initials in Spanish) accepted millions in campaign contributions from drug traffickers seeking clemency from Santos.

Rendon promptly resigned from the Santos campaign, and while the president acknowledged that traffickers had reached out to Rendón, he denied any quid pro quo, challenging Zuluaga and Uribe to offer proof.

Two days later, voters were whipsawed when a mysterious computer hacker employed by the Zuluaga campaign was taken into custody, accused of intercepting communications — even the president’s — surrounding the highly sensitive peace negotiations between government negotiators and FARC leaders in Havana.

Cellphone video and audio surfaced a few days later, appearing to show Zuluaga and the alleged hacker discussing the intercepts at a campaign office. Zuluaga says the recordings are fake, a “dirty trick” of the president.

Few doubt that the evolving peace deal with the FARC, the country's largest insurgent group, is at risk of collapsing if Zuluaga wins.

“Peace is close at hand,” Santos says in campaign commercials. “We can’t go backward.”

But surveys show deep ambivalent about the negotiations. While most Colombians want peace, said pollster Restrepo, “they’re pessimistic about the talks with FARC because they don't believe they’ll lead to a good agreement.”

Santos represents the negotiated solution. Zuluaga, like Uribe before him, represents a military one.

Pushing for peace

The United States views the FARC as the hemisphere’s most powerful terrorist organization and one of the largest drug trafficking groups in the Americas. Washington has sent at least $9 billion in security aid since 2000, more than anywhere else outside the Middle East, through “Plan Colombia.”

When Uribe was president between 2002 and 2010, his aggressive anti-insurgency campaign cut the FARC’s ranks by half and severely weakened the guerrillas, pushing them into more remote jungle areas.

Santos has pressed the campaign and killed several of top guerrilla leaders with help from the CIA and other U.S. agencies, using satellite-guided bombs to penetrate the jungle canopy.

“Peace without impunity,” is Zuluaga’s campaign pitch, and he insists that the FARC lay down its arms before continuing any talks.

This is a non-starter for the guerrillas, tantamount to surrender.

But defeating the FARC on the battlefield could take many more years, especially because the organization has begun to profit from a mining and oil boom in remote jungle areas under its control. It retains an estimated 7,000 to 10,000 armed fighters and continues to conscript children into its ranks.

After more than 18 months of formal negotiations in Cuba, the government and FARC leaders have agreed on three points of their five-point agenda: agrarian reform, the ability of FARC leaders to participate in electoral politics and an end to drug trafficking.

The last point, announced in Havana on May 16, is considered especially significant, because it is the first time the FARC has acknowledged its role in the drug trade. The group committed to implementing crop substitution programs in rural areas, replacing the coca and opium fields that have long helped finance its warmaking ability.

But coming just 10 days before the vote, the FARC announcement injected an extremely awkward dynamic into the race — criticized by other candidates as unseemly — in which Santos is both fighting the guerrillas and needing their help to push back against perceptions that the talks are a waste of time.

María Victoria Llorente, a security expert who directs the Ideas for Peace think tank, called it “a horrible marriage.”

A Venezuelan wild card

Yet another wild card is the increasing instability of Colombia’s neighbor to the east, Venezuela. In a debate this past week, Zuluaga said flatly that the country “is not a democracy” and harbors FARC “terrorists.” He said Santos has been “silently complicit” in allowing Venezuelan President Nicolás Maduro to erode democratic rule, and he said he would tighten border controls.

When Uribe was president, he and then-Venezuelan President Hugo Chávez often clashed, even bringing the countries to the brink of war. But Santos has declined to engage the blustery Maduro in verbal jousting and said that effective diplomacy requires “prudence.”

If Zuluaga wins and the embattled Maduro senses a political advantage in ratcheting up tensions, it could affect regional stability, said Adam Isacson, a Colombia expert at the Washington Office on Latin America.

“There is a high probability that Zuluaga would take Colombia back to a time when relations with Venezuela were more volatile,” Isacson said. “And if Zuluaga pulls the plug on the peace process, the presence of FARC on Venezuelan soil goes right to the top of the agenda.”

FARC commanders ordered a unilateral cease-fire through Wednesday to avoid “disturbing” the election.