A man waves the Colombian flag during a Nov. 30 demonstration to demand the immediate endorsement of the revised peace deal between the government and FARC guerrillas. (Guillermo Legaria/AFP/Getty Images)

After a half-century of war, peace has come to this long-troubled region of Colombia, and the change has been terrifying.

On Christmas Day, gunmen assassinated a rural activist from the leftist Marcha Patriótica party as he rode home on his motorbike. A member of the group was ambushed along the highway here in early November. The mutilated body of another activist turned up two weeks later in the same area.

The killings appear to fit a pattern of attacks on left-wing activists, indigenous leaders, human rights advocates and members of Marcha Patriótica, with the pace picking up in recent months as the government finalized a controversial peace accord with Marxist FARC rebels to end Latin America’s longest-running conflict.

By stalking grass-roots activists who are promoting the accord and pushing for its full implementation, the killers have sent a chill across the Colombian countryside and sown new doubts about the pact’s chances for success.

“We believed in the peace process, and we thought things would change,” said Jesús Tabárez, 74, who leads an association of small-farm owners here in the northern Cauca department, where six of his fellow Marcha Patriótica members were killed last year.

Peace activists make their way into downtown Bogota in October after trekking from Cali to urge swift passage of the peace agreement. A revised version of the deal was approved in November, but supporters cite a wave of killings in its wake. (John Vizcaino/REUTERS)

“The government isn’t protecting us,” Tabárez added. “We’ve traded one problem for another.”

Colombian authorities acknowledge that at least 58 community leaders and social activists were assassinated in 2016. U.N. observers and independent rights groups put the figure higher.

Only a handful of suspects have been arrested, but shadowy right-wing militias are widely blamed for the killings. Threatening pamphlets and fliers, signed by groups calling themselves “Black Eagles” and anti-communist “self-defense” forces, have turned up in small towns; they list names of local activists the groups consider “military targets.” Tabárez and others here say they have seen truckloads of black-clad gunmen riding around at night.

The assassinations are kryptonite to the fragile peace deal. It is a sprawling and multifaceted agreement, but at its core is a government commitment to transcend Colombia’s pernicious culture of political violence and finally bring the rule of law to the rural backwaters where drug trafficking and guerrilla warfare have long been a way of life.

The FARC, or Revolutionary Armed Forces of Colombia, has been fighting the government since 1964 and claims it took up arms only in self-defense. The government has assured the group that Colombia’s democracy has matured, and officials have pledged to protect the FARC’s right to fight for its leftist principles as a political party if it ceases to be an armed insurgency.

Now the guns of assassins are blowing holes in those promises.

(Jenny Starrs/The Washington Post)

Also central to the peace accord is the promise that long-marginalized groups — poor farmers, indigenous people and Afro-Colombians — will be able to fully participate in democratic politics.

“For what?” David Flórez, a Marcha Patriótica leader, said in an interview. “To end up getting murdered?”

Activists suspect soldiers and police are carrying out the killings on behalf of the powerful Colombian landowners and others who oppose the peace deal, and they say prosecutors and judges are too scared to stop them. They want Colombia’s highly touted intelligence agencies to pursue criminal suspects with the same alacrity as they did the FARC.

The government promises it will do so, especially once peace with the rebels frees up the resources it needs to dismantle the criminal organizations it insists are doing the killings.

But as the FARC’s roughly 6,000 troops prepare to move in the coming months into United Nations camps where they will disarm, rebel leaders are facing doubts from rank-and-file guerrillas who don’t trust the government — their lifelong enemy — to protect them.

If lower-ranking FARC fighters lose faith in the peace process, it increases the risk they will cache weapons and possibly rearm. They may be spurred to accept jobs as hired killers for Colombian drug traffickers. There is also the growing risk of dissident FARC factions splintering off to form new insurgent groups.

FARC leaders expelled five lower-ranking commanders last month from a unit heavily involved in drug trafficking, presumably because its members were refusing to demobilize.

The distrust of the government is well-founded. Colombian history does not inspire confidence.

Tabárez, the farmer, was a member of the now-defunct Unión Patriótica party, a civilian spinoff of the FARC that was used as a trial balloon by the guerrillas when they were weighing a peace deal in the 1980s.

The experiment ended in disaster: So many Unión Patriótica members were assassinated that the party was essentially wiped out. The extermination campaign was often cited by the FARC as evidence that the only safe way to be a leftist in Colombia was with an AK-47 rifle in hand.

Although the government of Colombian President Juan Manuel Santos acknowledges an uptick in violence, it says there is no evidence of a systematic, coordinated assassination campaign like the one in the 1980s.

Rather, said Juan Carlos Restrepo, Santos’s top security official, Colombia has entered a bumpy transitional phase in which leftist groups and community leaders are becoming more outspoken and therefore more vulnerable.

Protecting them, said Restrepo, “is a top priority for us,” but he said the government doesn’t have the resources to assign bodyguards and armored cars to everyone who feels threatened.

As FARC units pull out of areas such as Cauca, where they earned millions from the drug trade, illegal mining and extortion schemes, new criminal actors are rushing to fill the void and may attempt to kill or silence anyone who gets in their way, Restrepo and others say.

But Restrepo also said the government needs to push back against perceptions that the violence is spinning out of control or that every killing in notorious trafficking areas like northern Cauca has a clear political motive. The reality is often muddier.

After Jhon Jairo Rodríguez, a 33-year-old father of four, was fatally shot on the side of the road outside Caloto on Nov. 1, Marcha Patriótica claimed that yet another of its community leaders had been slain.

But his father, Manuel Rodríguez, said in an interview that his son rarely attended political meetings and was a lot more interested in motorcycles than land reform.

He acknowledged it was possible the gunmen had targeted his son simply to intimidate the community but said he didn’t want to put more of his family at risk. “I don’t know who killed him, but I’m not going to try to find out because I don’t want any more problems,” Rodríguez said.

Todd Howland, a Minnesotan who has directed the U.N. Office of the High Commissioner for Human Rights in Colombia for the past five years, said it will take time for police and prosecutors to develop the kind of relationships they need to effectively investigate crimes in remote areas where the government has long been absent. Quick implementation of the peace deal is critical, he said.

Howland said he has seen some improvements this year, but they are modest. Of the 61 murders of community leaders his teams verified in 2016, four have led to criminal prosecutions. “But in 2015 there were only two, and none the year before that,” Howland said.

Supporters of the peace deal are increasingly worried that Santos’s political capital is too depleted to allow him to implement the peace accord with the necessary rigor. The U.N. camps where the guerrillas are supposed to begin disarming aren’t ready, even though the government has had months to prepare.

Santos won last year’s Nobel Peace Prize for his determination to end a conflict that has left some 250,000 dead. But his final term expires in 2018, and when the campaign to replace him kicks off, the agreement with rebels is expected to once more become a political football.

Opponents say the accord is an outrageous political giveaway and a wrist-slap for FARC commanders guilty of atrocities.

The political fight has left Colombians badly divided. Voters narrowly rejected the first iteration of the peace deal in an Oct. 2 referendum, so the government and the rebels went back to the bargaining table. To avoid risking a second, potentially fatal defeat at the polls, Santos took the revised version to the Colombian Congress and won approval in late November.

Colombian rights groups say there has been a clear link between voters’ rejection of the first peace deal and the attacks against leftists that followed, because it “re-legitimized the idea of counterinsurgency,” said Carlos Guevara, director of Somos Defensores, which tracks political violence.

“It gave fresh oxygen to extremism,” he said, sending the message that “if you’re for peace, then you’re a supporter of the FARC.”

Guevara predicted an even bloodier 2017. “We’re entering the post-conflict phase,” he said. “But we’re starting it on broken legs.”