Correction: An earlier version of this story incorrectly identified Marc Lynch as a professor at Georgetown University. Lynch is a professor at George Washington University. The story has been updated.

U.N.-Arab League envoy Kofi Annan before a meeting at the U.N. offices in Geneva on July 20. (Fabrice Coffrini/AFP/Getty Images)

Kofi Annan’s plan to curb the violence in Syria hit a dead end this month, another casualty of an escalating conflict that shows no signs of abating.

But Annan’s failure may have taken another toll — on the reputation of a career peacemaker and, by extension, on confidence in the power of diplomacy to resolve what is turning out to be one of the most intractable crises to grow out of the Arab Spring.

World leaders and U.N. experts have commended Annan for showing the courage to take on what they term a diplomatic “mission impossible.” But among Syrian activists and Arab critics, he has been vilified as a shill for President Bashar al-Assad. Many of those close to Annan fear that his legacy is at risk and that it is time for him to confront reality and step down from his position as special envoy.

“I feel very sorry for Annan, not because I’m an old loyalist but because he has been dealt this hand,” said a senior U.N. official involved in Syria diplomacy, speaking on the condition of anonymity in order to comment candidly. “If I were him, I would be seriously thinking about resigning. Why keep banging your head against a brick wall when you’ve become a hated figure in social media around the world? And for what?”

That bitter assessment reflects a conviction among sympathetic observers that Annan is set to be a scapegoat to shoulder the blame for key powers, including the United States and its Arab and European allies, that have been unable to persuade or compel Assad to cease the killing, as well as Russia and China, which have blocked efforts at the United Nations to punish Assad for his conduct.

But critics say Annan has allowed himself to be used by Assad and the Syrian government’s Russian and Chinese patrons in a naive effort that has allowed authorities in Damascus to buy time to crush the opposition.

“There is a kind of happy convergence between Kofi’s willingness to try a thing that may make him look naive and the world’s wish to have him try this because it doesn’t have anything more effective and forceful that it is prepared to do,” said James Traub, author of a book on the former U.N. chief, “The Best Intentions: Kofi Annan and the UN in the Era of American World Power.”

‘The secular pope’

In March, after appeals from Secretary of State Hillary Rodham Clinton and other key players, Annan was asked by U.N. Secretary General Ban Ki-moon to come out of retirement and serve as a mediator in Syria.

A Nobel Peace Prize laureate — dubbed “the secular pope” by some — Annan seemed a natural choice, in part because he enjoyed the trust of all the key powers.

While Annan has been associated with some of the United Nations’ greatest failures, having headed up the U.N. peacekeeping department during the mass killings in Bosnia and Rwanda, he also racked up diplomatic achievements such as guiding East Timor to independence from Indonesia and, more recently, brokering a complex peace-sharing agreement in Kenya. He also had a track record of working with Assad.

In his upcoming memoir, Annan says he bore no illusions about Assad’s commitment to peace when he took on his latest assignment but also believed Assad was a “modern man” ready to initiate reforms in Syria.

Annan writes in “Interventions” that Assad’s response to the popular uprising “confirmed my more troubling suspicion that he was a man . . . willing to employ any means to retain power.”

In many ways, the peace plan Annan developed for Syria played to Assad’s strengths. It suspended talk of U.N. sanctions and reframed the U.N. debate from one that required Assad’s departure to one that would place him firmly at the center of any political settlement.

Asked by Assad what the transition would portend, Annan answered that it “would lead to whatever you agree at the negotiating table,” according to a diplomat close to Annan who was not authorized to speak publicly about the meeting.

April cease-fire

Shakeeb al-Jabri, a Beirut-based Syrian activist, said the April 12 cease-fire Annan brokered had provided tangible benefits, bringing about a lull in the violence and imposing constraints on Assad’s security forces, particularly in the area of Idlib.

But over time, Annan’s standing diminished as Syrian tanks shelled residential areas with impunity, forcing the United Nations’ unarmed monitors to suspend their patrols and undercutting the prospects for political talks. This month, demonstrators throughout the country carried banners calling for the “toppling of Annan the servant of Bashar and Iran.”

The opposition realized that Assad would not go peacefully and hoped Annan would come to the same conclusion.

“It seems that hasn’t happened yet,” Jabri said. The Annan plan is “nowhere,” he added. “It’s dead. It’s over.”

Salman Shaikh, a former U.N. official who serves as director of Brookings Doha Center, said Annan’s mediation was undercut by his instinctual faith in the power of diplomacy. “He would not do what was not in his instinct — to take a much more muscular approach to this, try to coerce the regime into submission. He believed he could turn the Russians around.”

“Nobody believes in the Annan plan, not in the region, not within the opposition, not even in Western capitals,” Shaikh added. “His credibility, in my view, is shot, particularly among the opposition on the ground, which is what counts.”

Officials close to Annan say that he was extremely disappointed by the failure of major powers to strike a compromise over the way forward in Syria and by the efforts of Persian Gulf states to sabotage the plan through the provision of arms to the opposition. But he is still trying to find ways to resuscitate the plan, they say.

“Nobody can blame [the opposition] for feeling outraged and frustrated,” said the senior U.N. official involved in Syria diplomacy. “We are all outraged and frustrated. We can’t seem to affect events on the ground, and every day we wake and realize it’s just slipping out of control, including Annan.”

Those sympathetic to Annan dispute suggestions that he had gone soft on Assad and his chief patron, Russia, noting that he pleaded with the Security Council to punish those who undercut his peace plan. He held an hour-long meeting with Russian President Vladi­mir Putin this month to press his case, and “he did not mince his words,” said the diplomat close to Annan.

“He told [Putin] very frankly, ‘You must realize that Assad is going down sooner or later, and you’ve got to cut him loose sooner or later,’ ” said the diplomat, who was present at the meeting.

In the end, there was no agreement to be had, and Russia and China cast their third veto of a Western-backed U.N. resolution threatening sanctions against Syria. In doing so, they effectively killed Annan’s peace efforts.

“In terms of judging Annan, he obviously didn’t succeed at the top line of what he was trying to do,” said Marc Lynch, a professor of Middle East politics at George Washington University. “But for everyone who mocked Annan’s idea for a brokered transition, it might end up looking a hell of a lot more attractive in retrospect than the kind of chaos we could see emerging if this takes a sharp turn for the worse.”