A Nuclear Deal for U.S. and Iran Slips Away Again VIENNA - By the time Secretary of State John Kerry and his Iranian counterpart checked into a luxury hotel near the famous beaches of Oman earlier this month, a long-sought deal that has eluded the last two American presidents to roll back Tehran's nuclear program seemed to be slipping out of reach. With a deadline approaching, Mr. Kerry thought the opportunity could be lost unless the Iranians finally offered a breakthrough compromise. But Mohammad Javad Zarif, the Iranian foreign minister, came with little new. Frustrated, Mr. Kerry said there was no way the United States would accept a deal that did not curb Iran's ability to produce enough fuel for a bomb within a year. The conversation grew heated. The two men, patricians in their own cultures and unaccustomed to shouting, found themselves in the kind of confrontation they had avoided during multiple negotiating sessions over the past year. "This was the first time there were raised voices and some unpleasant exchanges," said an American official, who like others requested anonymity to describe secret diplomacy. On Monday, as the deadline finally arrived, Mr. Kerry left another negotiating table in Vienna, having failed to bridge the divide. The last-minute offers he expected never arrived. And yet the two diplomats agreed that they may yet agree, and so they settled for a seven-month extension of the deadline in hopes that a new approach might enable them to find the middle ground that has escaped them. If anything, the last few weeks underscored a larger conclusion about the negotiations: If the deal had been left to Mr. Kerry and Mr. Zarif, and to their respective teams, it probably would have happened. The two men have developed a strong working relationship, and the flare-up in Oman a couple weeks ago underscored how much each wanted to get to a deal but could not. In the end, both were constrained by hard-line politics at home. Mr. Zarif, while friendly, outgoing and Westernized, had pushed to the very limits of his brief; he often warned that the final decision would be in the hands of the supreme leader, Ayatollah Ali Khamenei. And Ayatollah Khamenei, American intelligence officials had told President Obama and Mr. Kerry, was heavily influenced by the Revolutionary Guard Corps and his own distrust of the Americans. For his part, Mr. Kerry's position was complicated by the Republican midterm election victory and the fear of feeding the narrative that Mr. Obama was a weakened president. The bipartisan talk in Congress about new sanctions hung over the American negotiating team. And so did Israel's constant warnings that Mr. Obama was at risk of being duped. If Israel condemned any outcome as a bad deal, the label could stick in Congress. An agreement with Iran has hovered achingly out of reach throughout Mr. Obama's presidency, the foreign policy goal that could transform American relations with one of its most persistent adversaries and reshape the world's most volatile region. From the start, the story of the talks has been one of hopeful signs and dashed expectations, bursts of optimism occasionally piercing clouds of skepticism. Mr. Obama began reaching out shortly after taking office in 2009, writing the first of what would be four letters to Ayatollah Khamenei. It was not until last year's election of Hassan Rouhani, followed by his choice of Mr. Zarif, that doors really began to open and Mr. Obama authorized a secret channel to the two men through Oman. His envoys, William Burns and Jake Sullivan, both then top administration officials, traveled with little or no entourage, slipping into the back doors of hotels. Israel was kept in the dark for months, as were the French. The talks moved to New York in September 2013 under the cover of the United Nations" annual meeting. Mr. Zarif met Mr. Kerry in a closet-size room near the Security Council chamber, and the two exchanged private telephone numbers and email addresses, a channel they have used more than either has publicly admitted. Mr. Zarif helped engineer a telephone call between Mr. Obama and Mr. Rouhani, the first direct contact between American and Iranian leaders since the 1979 revolution. "It cost us when we got home," Mr. Zarif later noted. But the talks led to a deal last November to freeze much of Iran's nuclear activity in exchange for some sanctions being lifted while formal talks for a broader agreement were held. Wendy Sherman, the under secretary of state, led the new negotiations so persistently that she kept going even after rupturing a finger in a fall and later breaking her nose on a glass door in Vienna. Iran threw several curveballs. Ayatollah Khamenei said in a speech that Iran would ultimately increase its capacity to produce enriched uranium tenfold, rather than decrease it. "Zarif all but told us he didn't see that coming," an American official said. Mr. Zarif then surprised Mr. Kerry in July by proposing in an interview with The New York Times that Iran would simply continue the temporary freeze for seven years or so but dismantle nothing. "He's negotiating in public," Mr. Kerry fumed. Another American official said "it didn't even accord with what he was saying to us" privately. But it helped give Mr. Zarif room with hard-liners at home to extend the first deadline. Negotiators reconvened in late September in New York, but the Iranians told the Americans they would not consider real offers until after the midterm elections. The Americans said that was silly; the talks were not an issue in the elections. Mr. Kerry became more heavily involved. He began meeting with Mr. Zarif, either alone or, to keep the other partners in the loop, in three-way meetings with Catherine Ashton, the European Union envoy to the negotiations. As his party headed to defeat in the November elections, Mr. Obama gathered his team for several meetings in the Situation Room to consider his negotiating positions and opted to write another letter to Ayatollah Khamenei. With those positions finalized, Mr. Kerry and his team were empowered to press and see how far they could take the negotiations, in effect testing the Iranians. Mr. Kerry agreed to meet Mr. Zarif in Muscat, Oman, where the secret diplomacy had started. The Americans arrived in mid-November armed with a confidential eight-page paper outlining American ideas for closing the remaining gaps in many areas, which the Iranians were given to read but not to keep. The Americans had initially proposed to limit the number of operational centrifuges Iran would be allowed to retain to 1,500, down from the 10,000 spinning today. But with a side deal developing for Iran to ship much of its fuel to Russia, where it would be turned into fuel rods for the Bushehr nuclear plant, Iran's only operating commercial reactor, that number could rise to as many as 4,500 centrifuges. That was a function of "mathematics, not politics," one Western official said. "Essentially we were saying, "We'll meet you halfway." " But the Iranian side would not budge, leading to the ominous confrontation between Mr. Kerry and Mr. Zarif. Mr. Kerry flew to Vienna on Thursday for a final shot at meeting the deadline. The Americans sensed that Mr. Zarif had little leeway. Mr. Zarif and his aides warned that after the first meeting, the foreign minister would fly back to Tehran to get a bottom line from the clerics and military elite. The Americans said Mr. Kerry would also be leaving and told reporters to pack their bags. But in the opening session, Mr. Zarif told Mr. Kerry that there was no point in going back to Tehran if there were no new American offers on the table. Sounding frustrated, Mr. Zarif told the official IRNA news agency, "There were no remarkable offers and ideas to take to Tehran." To the Americans, Mr. Zarif's tactic looked like a squeeze play that was designed to elicit some last-minute concessions. There was debate among Mr. Kerry's team on how to respond, and some officials argued the secretary of state should call Mr. Zarif's bluff and leave for Paris anyway. He did not. "We're stuck," Mr. Kerry confided to Frank-Walter Steinmeier, the German foreign minister, as they convened on Saturday at the ornate Imperial Hotel. We were ready to go. "These are the hours of truth," Mr. Steinmeier said. As the clock wound down, the pace intensified. The French foreign minister returned to the talks. Sergey V. Lavrov, the Russian foreign minister, flew in, as did Saud al-Faisal, the Saudi foreign minister. But there was no breakthrough, just a set of "new ideas" for future discussions. On Monday evening, Mr. Zarif sounded preternaturally optimistic. He suggested the differences could be bridged in a few months. "The major problem is a compounded mistrust," he said, suggesting that had been gradually chipped away over the past year, though more among the negotiators, he seemed to say, than among their colleagues back in Washington and Tehran. But he added a warning: No one should treat this like a Cold War game. "If you are looking for a zero-sum game in nuclear negotiations," he said, "you are doomed to failure."