MEXICO CITY — Over years of struggle to end the half-century war in Colombia, world leaders from President Obama to the pope have celebrated and encouraged the peace process. But one political gadfly has been fighting it every step of the way.

Like a bleacher-seat heckler, former Colombian president Alvaro Uribe has been waging a one-man Twitter war against the government's peace talks with the left-wing FARC rebels. After the negotiations cleared a key hurdle on Wednesday, Uribe described the developments as a "coup against democracy."

Using the hashtag "Agreement of Impunity" (#AcuerdoDeImpunidad), he wrote that the terms would amount to "a new dictatorship backed by guns and terrorist explosives." He pushed out line by line his nine-point rebuttal.

He has tweeted pictures of advisers for his archrival, President Juan Manuel Santos, asking if they will be part of a transition team in the coming FARC government.

He has blasted U.S. Secretary of State John F. Kerry for applauding the peace progress.

He has stomped on any optimism for the future, in the tweet shown below: "Santos, it's not peace that's near, it's the surrender to FARC and the tyranny of Venezuela."

And that's just in the past two days, when he has tweeted or retweeted at least 96 times. With more than 4 million followers, his message has a broad reach.

"He's tweeting up a storm. It just doesn't stop," said Michael Shifter, president of the Inter-American Dialogue, a Washington think tank. "He's unrelenting and he's just pounding away."

Uribe's eight-year term, in which he aggressively battled the FARC, ended in 2010, but he has not drifted into ex-presidential obscurity, content with oil painting or charity work, like some of his American counterparts. He got elected as a senator last year, the first time a former Colombian head of state has gone that route. And he has remained a prominent opponent to Santos, whose popularity has sagged with a weakening economy and fears about the peace deal.

The current of fear and opposition to negotiations that Uribe has tapped into is one of the reasons why the peace process is still fragile. More than 220,000 people have been killed in the fighting among guerrillas, the government and right-wing paramilitaries, and millions more have been displaced. Many people want FARC guerrillas prosecuted for their crimes and thrown in jail, not let off if they admit to what they have done. The deal announced Wednesday would establish a truth-and-reconciliation process in which combatants who testified about their crimes would be eligible for "alternative justice" including fines and house-arrest-type conditions.

Santos has said that there will be a popular vote of some kind on the final peace agreement.

"It’s not going to be an easy sell to a large part of the Colombian population," Shifter said.

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