Colombian President Juan Manuel Santos, center, and his wife, Maria Clemencia de Santos, before presenting the FARC peace accord to the president of Congress in Bogota, Colombia, on Thursday. (John Vizcaino/Reuters)

HAVANA — Over four years of peace talks with the Colombian government, the country’s FARC rebels bargained for the best deal possible — and one that could convince their troops that the past half-century of guerrilla warfare wasn’t for nothing. But in wresting significant concessions from the government, including a launchpad into politics and a chance to skirt prison, the rebels have run the risk of sweetening their deal so much that Colombians won’t stomach it.

This was perhaps the key masterstroke of President Juan Manuel Santos’s insistence that the peace deal be contingent on Colombian voter approval. He has set that vote, formally a “plebiscite,” for Oct 2. The entire deal is riding on the outcome.

Santos and his negotiating team have long warned Colombians that peace would have a price, as well as a heavy dose of what Colombians call “toad swallowing,” i.e. bitter medicine. The government insists it has secured the best deal possible with the guerrillas, and with the accords now finalized there will be no chance of making revisions. If voters reject the agreement, the pact crumbles and the war will resume.

[Here are the details — critics would say the devils — in Colombia’s peace deal with FARC]

FARC commanders were no fans of this strategy. They wanted the deal to be ratified through a more limited consultation process — a special assembly — whose outcome would have been more predictable and easier to control. And like many of the peace deal’s supporters, they worry that Santos’s low approval ratings will hurt them at the ballot box.

Yet they have also feathered their beds with significant concessions from the government, guarantees that Santos opponents caricature as a giveaway to FARC “terrorists” who got rich on the drug trade and committed horrible atrocities. Now the guerrillas are ducking punishment and getting a golden parachute into politics, opponents say.

Under the terms of the agreement, FARC will be afforded nonvoting representatives in Congress through 2018, where they will be able to weigh in on matters related to the implementation of the accords. Then come the biggest toads: a minimum five seats for FARC in the 106-member Colombian Senate and five more in the 166-member lower chamber for two legislative terms through the creation of new voting districts. FARC, which has yet to reveal the name of its future political party and can’t form one until it fully disarms, will have to compete for seats on its own merits after that.

[The staggering toll of Colombia’s war with FARC rebels, in numbers]

Opposition senator Alfredo Rangel called these final concessions by the government “shameful.”

The rebels insist this pact is fair, given that so many leftists leaders, including FARC chief negotiator and former congressman Ivan Marquez, were forced out of democratic politics a generation ago by violence. Thousands of members and supporters of the Patriotic Union party, formed by FARC and other Colombian communists, were wiped out in the 1980s and '90s by paramilitary gunmen.

Still, it will not be hard for the peace deal’s detractors, led by powerful former president Álvaro Uribe, to depict the guarantee of 10 unelected legislative seats as an unconscionable freebie. Colombians who know FARC leaders from grainy “wanted” posters and jungle videos may have trouble accepting them as respectable lawmakers.

Another element that could trigger public resentment: Demobilized ex-combatants will receive a monthly government stipend nearly equal to Colombia's minimum wage for a two-year period after the accords. They will also be eligible for onetime cash payment of about $2,500 -- a significant sum in Colombia -- to start a business.

Uribe and other opponents of the deal have also attacked it on the grounds that it offers “amnesty” to FARC commanders charged with murder, kidnapping, drug trafficking and other crimes. The accords will establish a parallel justice system akin to a truth-and-reconciliation process, wherein guerrillas and members of Colombian security forces and other combatants can serve time at halfway houses, work farms and other alternatives to prison.

In his speech Wednesday, Santos seemed hard-pressed to push back, insisting there would be “no immunity” for the worst offenders. “They will be investigated, judged and sanctioned with several years of restrictions on their freedom. They’ll have to tell the trust — the whole truth — and make reparations to their victims,” Santos said. “And if they don’t, they’ll go to jail for up to 20 years.”

Adam Isacson, a Colombia expert, said the justice agreement and FARC’s return to politics are the two biggest points in the peace deal that will be “hugely unpopular in Colombia and carry a political cost for Santos.” But he said FARC has arguably given up more in the negotiations, since it scratched much of its wish list items, including land reform, full amnesty and an end to forcible coca eradication.

“I think the FARC gave some ground when it became clear that too much intransigence would only empower the far right in Colombia,” said Isacson, a security analyst at the Washington Office on Latin America. “They were careful to bend the process, to get what they could, but not break it.”

On Oct. 2 the government and the rebels will find out whether they found the right balance, or if their accord will die on arrival.