Colombian presidential candidate Ivan Duque, for the Democratic Center party, gives his thumb up after voting at a polling station in Bogota during the first round of the presidential election in Colombia. (Luis Acosta/AFP/Getty Images)

BOGOTA, Colombia — In first round presidential elections Sunday, Colombians are hitting the polls to choose who they want to guide Latin America’s third most populous nation through a troubled moment marked by soaring cocaine production, a shaky peace accord with a Marxist rebel group and the influx of Venezuelan migrants flooding over the border to escape an economic crisis next door.

The conservative 41-year-old lawyer Iván Duque was leading in pre-election polls, followed by the progressive 58-year-old economist and ex-mayor of Bogotá, Gustavo Petro.

Other candidates are a mathematician who was the centrist mayor of Medellín, Sergio Fajardo, and a former vice-president, Germán Vargas Lleras, on the center-right.

No candidate is expected to win outright on Sunday, and there will likely be a run-off, probably involving Duque and Petro. That vote would come June 17, and it would give Colombians a choice between right and left, one they haven’t had for decades.

Colombia is polarized. A 2016 peace accord led to the demobilization of thousands of fighters from the FARC rebel group last year, but while some Colombians want to forgive and move on, others are frustrated, insisting on harsher punishment for FARC leaders than is currently pending.

And a wave of poor Venezuelan migrants crossing illegally into Colombia is challenging an under-employed work force.

In the post-conflict era, the long-time American ally’s security issues are changing. Colombia’s next president will have to deal with a major increase in the amount of land under coca cultivation. After two decades and a U.S. package of over $10 billion in aid to fight against drug-trafficking groups, a smattering of violent, criminal organizations has arisen with the endof the fighting. Peace talks with the ELN, a smaller rebel group, appear fragile.

“If Petro were to win, it could create big problems for Colombia’s relations with the United States, least because I would think Trump’s immediate reaction to Petro would be very negative,” said Philip Paterson, a Latin American analyst at Oxford Analytica. “We might see a lot more frustration between Washington and Bogotá in terms of Washington pushing for coca crop eradication programs – which I think Petro would be far less likely to follow through on, where Duque would do it enthusiastically.”

The issues on voters’ minds reflect a Colombia that more and more resembles its South American neighbors, where ire toward corruption, frustration over access to effective healthcare, and attention to environmental issues are competing with Colombia’s age-old political debates of how to tackle drug-trafficking and stop armed conflict.

For voters, Duque represents a nostalgic return to the hardline security stance of former president Alvaro Uribe. Duque has called for harsher punishments for FARC leaders, who currently face restricted liberties if jurors find they tell the truth in a special tribunal.

He was elected in 2014 as a senator in Uribe’s Centro Democratico party. Before that, he worked at the Inter-American Development Bank in Washington.

Duque argues that Colombia’s economy is hamstrung by regulations and taxes on private enterprise. He’s calling for tax cuts and reductions in public spending.

Alexandra de Brigard, a 47-year-old architect, said she supports Duque with the hope that he will restore Colombia to what it was before outgoing President Juan Manuel Santos took office in 2010.

“I’m from the generation that lived a really horrible and violent chapter of Colombia’s history. Uribe saved us when it seemed like we had no hope,” she said.

“Santos did the exact opposite of what he promised, the exact opposite of Uribe,” she added, reflecting many pro-Duque voters’ regret and frustration that the second-term Santos broke the continuity of Uribe’s hardline security policy with FARC.

Victor Manuel Sierra, also 47, says he’s voting for Duque because his 25-employee cable wire business is suffocating under the weight of high taxes.

Detractors insist that behind Duque’s moderate rhetoric are staunch, ultra-conservative sectors backed by regional business elites.

“Duque represents a defense of the status quo,” said Alvaro Villarraga of the Democratic Culture Foundation.

Petro is a former member of a left-wing armed movement known as M-19. He worked for its political wing until it disarmed in 1991 as part of a peace process.

Elected to the senate, Petro gained a reputation for exposing corruption. In 2011, he was elected as mayor of Bogotá.

Petro wants to dismantle Colombia’s mining and oil sector and replace it with renewables, as well as strengthening the agricultural sector – where many of the rural poor are employed.

Petro has said he’d buy land if landowners won’t pay his proposed higher taxes on under-used property. His opponents cry expropriations, equating him with Hugo Chavez of Venezuela.

“He’s talked about wanting to wind down coal and oil in three years, which I think is extremely ambitious and unlikely to happen in reality,” says Paterson. “I certainly don’t think he would be hostile to business. He’d still be trying to encourage international private investment into Colombia.

“This idea that he’s the ‘New Chavez’ is way off the mark.”

His supporters see the upside to a leader with leftist sympathies who presents himself as an outsider. “I like Petro for his ideas: his defense of the environment, and offering free higher education,” says 34-year-old political scientist Andrés Ignacio Sánchez, who is currently unemployed.

“Forever now he’s gone against institutions and the way they currently work.”