New problems, old fears ahead of Colombia's presidential election The peace process, once again, is front and center.

Colombians are heading to the polls to elect a new president Sunday, and entrenched polarization on how to handle the country's fragile peace process and growing refugee crisis is front and center.

Six candidates are jockeying to become the newest resident in the presidential palace, as current President Juan Manuel Santos is term-limited from running for office. A former defense minister who's been president since 2010, Santos shepherded a peace process that gave the Revolutionary Forces of Colombia -- better known as FARC for its initials in Spanish -- a shot at a place in mainstream politics, in theory ending a five-decade-long war between the guerrilla group and the Colombian people.

But the disparate campaigns and opposite takes on issues speak to a growing division within Colombian society on how big of a role they want the FARC to have in government, and how they want the government to deal with the growing economic and social problems, including an influx of Venezuelan refugees fleeing poverty and hunger across the border.

Sunday's vote will define the country's politics for years to come -- like in the United States, the presidential term in Colombia is four years, with the possibility of serving two terms. And changes could be dramatic -- polarization between right- and left-wing politicians has only increased after the peace agreement was signed.

If none of the candidates get 50 percent plus one vote or more, the top two vote-getters will move on to a runoff election June 17.

The stakes

The Colombian peace agreement, signed in Havana in the fall of 2016, remains very controversial, with many condemning the power it gives former FARC guerrilla members, and some others saying it is needed if the South American country is to heal after half a century of war.

Among the most controversial points of the agreement: the return of FARC combatants to civil life without fear of imprisonment and the inclusion of the FARC in national politics.

The deal also calls for demilitarization and the restitution of land used by guerrillas for the production of cocaine.

With several candidates campaigning on dismantling or renegotiating the deal, and others attacking the FARC and its leaders, some fear the hope for peace that the agreement seems to bring will not last.

“If this peace process ends it will be the start of huge problems ... the FARC doesn’t need to be begged to go back to violence,” said Malia Lobete in Medellin, the second largest city in the country.

Lobete knows what she's talking about -- the conflict between the Colombian government, the FARC, other guerrilla and paramilitary groups and drug cartels left more than 220,000 people dead and displaced another 5 million. More than 25,000 people vanished during the conflict, according to Colombia's National Center for Historical Memory.

On top of the old fears, there are new problems, as an increasingly dramatic border crisis threatens to upend Colombian prosperity. More than 30,000 Venezuelans are estimated to cross the porous Colombo-Venezuelan border every day to buy groceries, go to school, catch buses to other Latin American countries or find work in border towns.

Many live in overcrowded shacks, working for pennies. Mauricio Franco Trujillo, the head of security for the border city of Cucuta, told ABC News recently that his city -- and the border -- were at the point of total collapse.

The candidates

IVÁN DUQUE - considered the front-runner, former Sen. Duque is the leader of the right-wing Democratic Center party and has the support of former President Alvaro Uribe. Duque has said he wants to renegotiate terms of the peace agreement, which he opposed in 2016. Duque has campaigned on banning the FARC from political engagement and has advocated for prison time for former FARC commanders.

GUSTAVO PETRO - a one-time guerrilla leader and mayor of the capital city of Bogota, Petro is the main left-wing candidate running this Sunday. In a country wary of left-wing leaders, who are often supported by unpopular guerrilla groups, Petro has managed to rally those disappointed by decades of right-wing rule, becoming popular among young voters. Still, his dissenters compare him with the late Venezuelan President Hugo Chavez, stoking fears that Colombia could go down the same economic spiral affecting Venezuela.

SERGIO FAJARDO - the former mayor of Medellin and governor of the state of Antioquia, Fajardo, seen as a centrist candidate, is a proponent of the peace accord and has a long history of favoring the integration and rehabilitation of former guerrilla combatants into society.

HUMBERTO DE LA CALLE - a former vice president of Colombia and the chief negotiator of the FARC peace accord, Calle is the candidate for the Liberal Party, one of Colombia's oldest, strongest and more traditional political parties. Along with the Conservative Party, the Liberals defined Colombian politics in the 20th century.

GERMAN VARGAS LLERAS - Lleras served as vice president in Santos' government. While a far-right candidate, he has said he will respect the peace agreement with the FARC.

JOSE ANTONIO TRUJILLO - the evangelical pastor, who pollsters give a very low chance of winning, has said, should he be elected, he'd be harsher in dealing with the FARC.

ABC News' Kirit Radia contributed to this story.