Young people marching against fraud in some formats of vote counting in the last presidential elections of Colombia on May 31, 2018. Sebastian Delgado | SOPA Images | Getty Images

Last month, Colombia held its first presidential election since the government signed a historic 2016 peace agreement with guerrilla movement the Revolutionary Armed Forces of Colombia. The poll was set to be a referendum on that deal, but it proved inconclusive, and the country is heading to a runoff. The first round of elections ended with two leading candidates who will face off on June 17: Conservative Ivan Duque led with 39 percent of the vote in the first round, and leftist Gustavo Petro followed with 25 percent. Centrist Sergio Fajardo came in third place with 23.8 percent of the votes, and his supporters will now help decide the run-off outcome. Petro, a former guerrilla himself, could find the vote difference with Duque too large to overcome, according to Paulo Gregoire, a Bogota-based analyst for geopolitical intelligence firm Stratfor. "I think Petro will have a tough time because, to win the election, he would need over 90 percent of votes from Fajardo's supporters," Gregoire told CNBC over the phone. In fact, Fajardo has already said he would not vote for either candidate. Still, a poll by think tank the Latin American Strategic Center of Geopolitics held between May 29 and June 6 showed that Petro was now just 5.5 points behind Duque in the elections.

What's at stake

One of the main issues at play in the election is the peace agreement between the government and the rebel group, which is known as FARC. Duque opposes the peace deal, claiming that it is too lenient on the former guerrilla members and has campaigned to modify the amnesty clause for them. On the other hand, Petro is supportive of the peace agreement, and is unlikely to change the terms. The potential fallout of Duque's proposed modifications could result in more members of the rebel group mobilizing in the face of legal uncertainty. Former FARC fighters have already splintered off and created a new rebel group, the United Force of the Pacific. Increasing doubts over the peace agreement could push more people into the new rebellion. "It is important to remember that around 300 to 500 FARC members chose not to join the initial peace agreement in the first place," Gregoire warned. It would not be easy for Duque to modify the agreement even if he comes into power, however, as the deal is protected by the country's constitutional law. One way he could do it, according to Gregoire, is by calling for a referendum.

Venezuelan Crisis

The two leading candidates would also move the country in opposite directions when dealing with the crisis in Venezuela. Approximately 1 million Venezuelans have entered Colombia since the country fell into an economic crisis in 2017. Duque's campaign asks Colombian voters to "Vote so that Colombia does not become another Venezuela," and Gregoire said that Duque would take a tougher stance against the neighboring country in terms of sanctions, in the form of backing the U.S.-imposed penalties on the Venezuelan oil industry. A Duque victory in the elections — as appears probable — would likely see the relationship between the two countries become even worse, Gregoire said. A Petro victory, however, would probably mean Colombia employs softer approaches regarding Venezuela. The Stratfor expert said a significant portion of Colombia is wary of Petro's historically close ties to Hugo Chavez, however, and they fear a leftist presidency will lead to their country becoming similar to Venezuela. Petro has become more critical of Venezuelan President Nicolas Maduro recently, but, in any case, his foreign policy toward Venezuela is likely to be much more passive than Duque, Juan Felipe Celia, assistant director and Colombia lead at think tank the Atlantic Council told CNBC.

Potential economic impact