Conservative Ivan Duque captured Colombia’s presidency Sunday, bringing to power a U.S.-educated 41-year-old whose victory promises an aggressive new era in the drug war and could upend a historic peace deal that ended Latin America’s longest running insurgency.

With nearly all the votes counted, Duque held a commanding lead of 54 percent to 42 percent. Turnout was 53 percent of voters, higher than in other recent Colombian elections.

By winning Sunday’s vote, Duque — who spent years studying and working in Washington — stopped the rise of his leftist opponent, Gustavo Petro. At a time when the production of coca — the source of cocaine — is soaring to record highs here, Petro, a former guerrilla turned senator turned mayor of Bogota, had pledged a break with what he called the “militaristic” drug war backed by the United States.

In contrast, Duque’s win could herald a return to more forceful tactics. The United States has spent $10 billion in two decades fighting coca growth here — only to find it higher now than at the launch of the campaign. U.S. officials see Duque — a protege of right-wing former president Alvaro Uribe, who launched a widespread offensive against guerrillas and narco-traffickers in the 2000s — as a reliable partner. He could bring back a version of the controversial practice of aerial spraying, banned in 2015 for health reasons.

Duque — who also pledged to lower corporate taxes and boost police forces — brings with him this nation’s first female vice president, former defense minister Martha Lucia Ramirez, 63.

Particularly after his first-place finish in the first round on May 27, Duque sought to assuage concerns that his presidency would rekindle national tensions. Late Sunday, he addressed cheering supporters in central Bogota, but he also spoke to his deeply polarized nation.

“Let’s turn the page of polarization and fights,” he said. “I do not recognize enemies in Colombia. I will not govern with hate or have hate against any Colombian. In my mind and heart, there’s no thirst for vengeance or reprisals.”

Yet Duque’s victory potentially endangers the 2016 peace accord struck with the former Revolutionary Armed Forces of Colombia (FARC), for which outgoing President Juan Manuel Santos won the Nobel Peace Prize. A critic of the accord, Duque has stopped short of saying he would tear it up. But he has called for “structural changes” — in particular that the group’s former leaders who have been granted seats in Congress should be tried for war crimes.

Critics fear such changes could kill the deteriorating peace process, sparking a new wave of violence at a time when deaths in post-conflict zones are jumping again. Yet on Sunday, Duque voters said they backed a harder line.

“The peace accord was a lie,” said Rodrigo Pimentel, 72, a Bogota doctor who voted for Duque. “Internationally, everyone was in favor of it. But not here. How can the same people who killed so many, who were narco-traffickers, sit in our Congress?”

Late Sunday, Duque pledged to push forward with major aspects of the peace accord — including reintegration of former combatants. But he also reiterated his call for changes to the deal. 

“The peace we long for requires corrections,” he said.

Duque’s victory additionally marked the triumphant return of Uribe to the apex of Colombian politics. A divisive figure whose tenure in the 2000s was marred by allegations of links to right-wing death squads, Uribe is seen as the primary architect of Duque’s rise to the presidential palace.

In fact, for many Colombians, Duque appeared to come out of nowhere. Early in his career, he worked as Uribe’s assistant and adviser. After studying and working in Washington for years, Duque came back to Colombia at Uribe’s urging, where he helped catapult the young conservative to a senator’s seat in 2014.

The question facing Duque will now be how much, if at all, he can emerge from Uribe’s shadow — and resist calls from some in his base to completely break with the peace accord.

“Duque’s style is pragmatic,” said Michael Shifter, president of the Inter-American Dialogue, a Washington-based think tank. “He does have the ability to overcome some of the divisions in the country, but if he goes forward in rolling back significant aspects in the peace accord, that could create more tension, more division.”

The outcome has an additional winner farther north: Washington. Educated at American and Georgetown universities, Duque spent years living in Chevy Chase, Md., and working for the Washington-based Inter-American Development Bank. He hails from a staunchly pro-American segment of Colombian politics.

“You could call him a ‘D.C. Colombian,’ ” said Juan Felipe Celia, a Colombia expert at the Atlantic Council, a Washington-based think tank.

During a bitter campaign, Duque’s camp sought to portray Petro as a harbinger of far-left ideas whose policies would turn Colombia into another Cuba or Venezuela. Petro — who has spoken fondly of the late Venezuelan firebrand Hugo Chávez — fought back against such characterizations and sought to moderate his line. Yet on Sunday, many voters appeared to be backing Duque in part to stop Petro’s ascent.

“Petro is another Maduro,” said Marta Quintero, a 54-year-old Bogota real estate agent, referring to Venezuela’s President Nicolás Maduro, whose country is confronting crippling hyperinflation and soaring hunger. “All you need to do is look over our border, at Venezuela, to see that the left is no solution.”

Yet in a country that has always elected conservative presidents, Petro went further than most analysts thought possible, winning more votes Sunday than any left-wing candidate in Colombian history. That he came so close to the presidency underscored a strong and growing disaffection with inequality, poverty and corruption — and potentially laid the foundation for a stronger challenge from the left four years from now.

Besides the drug war, one of the biggest challenges facing Duque is the resurgent National Liberation Army (ELN) — a guerrilla force that has muscled into territory once controlled by the FARC. Though suggesting he is open to dialogue, Duque has called attempts to push peace talks while the ELN still engages in criminal activity “a joke.”

To halt the march of the peace process with the FARC, Duque simply needs to drag his feet. Even Santos, who struck the deal, was unable to push many of the deal’s key provisions through Congress, leaving it up to Duque to push them through — or not.

“The fact is Duque really doesn’t need to do anything to block the accord,” Celia said. “All he really has to do is do nothing.”

Dylan Baddour in Bogota and Rachelle Krygier in Caracas, Venezuela, contributed to this report.