VIENNA — With his marathon negotiations to prevent Iran from building a nuclear weapon, Secretary of State John Kerry has inched tantalizingly close not just to a single historic deal but to what he views as the linchpin for possible future diplomatic breakthroughs across the Middle East, particularly in combating the Islamic State group.
“I think that there’s an opportunity here to galvanize people, hopefully, into a common-sense approach,” he said in a recent interview with the Globe. “Who knows whether or not the Iranian agreement, if it were achievable, could open some doors into that?”
Kerry’s words are further evidence of the habitually optimistic outlook that helps drive his determination to negotiate throughout this weekend with the Iranians, even after 15 straight days of talks — which have involved at least 51 meetings and 46 hours sitting at the negotiating table — with no deal.
It has been, in other words, a show of vintage Kerry: a belief, sometimes against evidence, that more hard work and more negotiation can bridge profound divides between mortal enemies.
Kerry has now spent more consecutive days negotiating abroad on one issue than any of his predecessors since Henry Kissinger spent 28 days seeking Middle East peace in 1974, according to State Department historians.
On Saturday, negotiators continued meeting but with no sign of an imminent breakthrough, with Kerry writing on Twitter the two sides “still have difficult issues to resolve.”
The possibility that an Iran deal could spawn further progress in the region excites Kerry. Creating stronger resolve in regional powers to fight the Islamic State would be at the top of the list of possible benefits, he said, and the countries meeting here could work to do more.
“That’s what I want to put to the test,’’ he said. “It’s clear to me that if an agreement is successfully reached, satisfactory to everybody, a conversation might be able to begin.
“I don’t want to make any predictions,” he added. “I’m not going to tell you it’s a sure bet. But I do think there’s a conversation in the waiting. And that’s one of the reasons why I’m so concentrated on trying to get this done.”
If he successfully engineers a pact with the Iranians, it would represent just the sort of sweeping, legacy-building accomplishment that has eluded Kerry throughout most of his career, while giving the Obama administration a victory on a world stage that has proved almost uniformly inhospitable to US diplomatic efforts.
Kerry has been stymied in multiple trouble spots, especially in Ukraine, Syria, and the Israel-Palestinian conflict.
In personal terms, Kerry is seeking an accomplishment that is bigger than winning his former US Senate seat, or rising to his Cabinet-level job. He wants to use his talent for nurturing personal relationships, his belief in international deal-making, and US leadership to make the world a better place — the kind of exclamation point on a career that might make up for his stinging defeat in the 2004 presidential race.
Aides and former negotiating partners describe him as an eternal optimist, playing the role of cheerleader during negotiating setbacks and constantly reminding them to be hopeful. Kerry has an enormous faith in his own ability to negotiate and cut big deals, using his personality, charm, and patience.
“In his inner self, I think he has a neon [sign] next to his mind saying, ‘Failure is not an option. Failure is not an option. Failure is not an option,’ ” Palestinian negotiator Saeb Erekat, who spent countless hours with Kerry trying to achieve peace with the Israelis, said in an interview.
“He will do everything humanly possible to reach this agreement,” Erekat said.
But he has had a frustrating series of negotiating partners — from the Israelis and Palestinians to the Iranians and the Russians, a difficult cast on which to pin hopes for a legacy-cementing achievement.
And Kerry, who maintains his habit of hard work even as he hobbles around on crutches, has sometimes had to recognize that no amount of trying on his part can solve problems if his negotiating partners won’t go along.
An Iran nuclear agreement’s power to serve as a springboard for solving other regional problems would depend on the strength of the deal, and whether it is seen as providing a lasting promise of nuclear security, say specialists.
“It’s unfortunate. He comes so close, and then certain things in the world happen,” said Shahid Ahmed Khan, who served as finance cochairman of Kerry’s presidential bid and later traveled with him to India and Pakistan.
“But most likely, this deal will happen,” he added. “If this comes through, Kerry should be nominated for a Nobel.’’
But what Kerry supporters see as his strength — his endless energy and enduring optimism — his critics see as a problem, particularly given the negotiations with a regime that has been an avowed enemy of the United States.
“I’ll always give John credit for tenacity and trying,” Senator Lindsey Graham, a South Carolina Republican who worked with Kerry on several issues, said in an interview. “But a lot of people feel sometimes that he gets too eager, that he can’t walk away. . . . John’s fatal flaw, I believe, is he wants things too badly.”
Graham, who is running for his party’s presidential nomination, credited Kerry for an interim deal — which put a freeze on Iran’s nuclear program in exchange for modest sanctions — that has worked better than he expected. But he said the final deal, which could allow Iran to resume the pursuit of nuclear weapons after 10 or 15 years, would cause further disruption across the region.
“We went from dismantling their program to ensuring they are a nuclear nation,” he said. “We are about to launch a nuclear arms race in the Middle East.”
If the Iranian deal falls apart, there are few other major foreign policy challenges on the horizon that Kerry could turn to with much hope of success. He and Energy Secretary Ernest Moniz have been working on some climate-change issues, but there are fewer big things — and less time to address them — left for him to tackle.
“Sometimes things have to align in history, at a moment in history, to be able to do something,” a senior US official said last week. “We are probably closer than we’ve ever been because there is more of an alignment of that moment in history. But whether it clicks into that final cube, we don’t yet know.”
In the interview with the Globe in Boston last month, as he recuperated from a broken leg and prepared to return to the Iran talks, Kerry said he had begun sketching out new approaches on addressing the conflict in Syria and the Islamic State.
He said that while the negotiations with Iran have been tightly focused on curbing its nuclear program in return for sanctions relief, “we’ve had some conversations about the region, obviously.”
Iran’s foreign minister, Mohammad Javad Zarif, has also talked recently about the potential for continued cooperation, particularly on fighting the Islamic State.
“Entire countries are being torn to sheds by roving bands of hooded men with no regard for the sanctity of human life,” Zarif wrote on Thursday in the Financial Times, a London-based newspaper. “To deal with this alarming challenge, new approaches are an imperative.”
Some outside observers question Kerry’s premise, that a deal with Iran would change the complexion of the Middle East. But they say that whether he succeeds or fails, Kerry should quickly turn his attention to combating the threat posed by the Islamic State, which also is known as ISIL.
“If Kerry solves this one, he better get more serious about ISIL because we are flailing on that one, especially in Syria, where his hope for a diplomatic solution in dealing with [President Bashar al] Assad has in fact been part of the problem,” said Michael O’Hanlon, a foreign affairs specialist at the Brookings Institution.
“In fairness, an Iran nuclear deal would be a major accomplishment,” he added. “I see the contours of the deal as mediocre . . . but still much better than the alternatives. And I admire his doggedness and commitment.”