THE resounding victory of Hassan Rohani, the most moderate and outward-looking of the presidential candidates deemed fit to contest the election by the supreme leader, Ayatollah Ali Khamenei, has raised hopes for a nuclear deal between Iran and the international community. As the Islamic Republic’s nuclear negotiator for nearly two years from October 2003, he showed a degree of flexibility that was depressingly absent in the most recent talks between Iran and the UN Security Council’s five permanent members plus Germany (P5+1).

Mr Rohani seems pragmatic enough to know that Iran needs relief from sanctions to revive its economy, and that a more constructive negotiating stance on the nuclear programme will be needed to get that. Nevertheless, the change in Iran’s top civilian office is unlikely to bring an end to the interminable Iranian nuclear crisis.

Even if Mr Rohani wanted to do the kind of deal that would be acceptable to the West (and there is nothing in his past to suggest that he might), the guiding hand behind Iran’s nuclear policy will remain that of the supreme leader, whose introspective, suspicious view of the world outside Iran has not changed. The die is already cast: nothing is likely to stop Iran getting the bomb if and when it decides it wants one.

The last set of talks between the P5+1 and Iran, the fifth of the current round of negotiations, were in early April and ended on a downbeat note. They followed a proposal in February to allow a modest easing of sanctions in exchange for restrictions on Iran’s uranium-enrichment programme and more comprehensive inspections by the IAEA. Intended as a prelude to a more far-reaching deal, the offer represented a slight softening of the six powers’ position, by allowing Iran to keep a small amount of uranium enriched to 20% (for use in a reactor to make medical isotopes) and calling only for the suspension of enrichment at Fordow, a plant buried deep within a mountain, rather than its closure.

Iran’s negotiator, Saeed Jalili (an unsuccessful presidential candidate close to Mr Khamenei), replied that he wanted a suspension of all sanctions in exchange for only a temporary halt to 20% uranium enrichment, an impossible demand.

Mr Rohani’s election means the next round of negotiations will be conducted in a better atmosphere. But to what end? The answer is that the process serves a purpose for everybody. For Iran, the continuation of talks is a means of getting some easing of sanctions in exchange for concessions that will have little impact on its nuclear programme. For America and its allies, the absence of progress up to now has kept the international community lined up behind sanctions. Both sides, preferring to avoid a military confrontation, have an interest in demonstrating that the diplomatic path to a solution has not yet reached a dead-end.

Yet the inconvenient truth is that while the talks seem destined to continue, Iran is close to what is known as “critical capability”—the point at which it could make a dash to produce enough weapons-grade uranium for one or more bombs before the IAEA or Western intelligence agencies would even know it had done so. Despite the severe economic pain that the tightening of sanctions has inflicted on Iran’s people and their evident desire for change, Iran’s strategic calculus has not shifted. The nuclear programme is worth almost any sacrifice because it guarantees the regime’s survival against external threats, as America’s differing policies towards Libya and North Korea illustrate.

Speeding up

How close is Iran to critical capability? British and American intelligence sources think it is about a year away from having enough fissile material to make a bomb and further still from mastering the technologies to make a nuclear warhead small enough to fit onto one of its Shahab-3 ballistic missiles and carry out the tests needed to be confident that the system works.

But two of the most respected independent analysts—David Albright, a former UN weapons inspector who is president of the Institute for Science and International Security and Greg Jones, a RAND Corporation researcher who writes on Iran for the Non-proliferation Policy Education Centre (NPEC)—believe that time is running out more quickly. Mr Albright thinks that by mid-2014 Iran will be able from a standing start to produce enough fissile material for a single bomb in one or two weeks. Mr Jones reckons that later this year Iran will be able to produce within about ten weeks enough weapons-grade uranium for a couple of nuclear weapons.

If Iran has a small clandestine enrichment facility designed to enrich uranium from 20% to 90% (highly enriched weapons-grade uranium, or HEU) it could quite soon be able to manufacture enough material for five bombs in about 14 weeks using a new generation of advanced centrifuges it has already begun to install in its main enrichment site at Natanz. Mr Jones, in a recent report for NPEC, says that although a secret facility would put Iran in breach of IAEA safeguards “the time needed for Iran to produce HEU by this method is becoming so short as to make it doubtful that any effective action could be taken before Iran obtained a nuclear weapon.”

For both Mr Albright and Mr Jones, what matters most is the relentless pace at which Iran is adding to its enrichment capabilities and thus the speed at which it can produce the fissile material needed for an implosion device, the most common form of nuclear bomb. As Mr Albright puts it, the critical component for “a fissile-material dash” is the quantity and quality of Iran’s centrifuges. Despite wide-ranging attempts by the West and Israel to delay or sabotage the nuclear programme, Iran has installed around 9,000 new centrifuges at Natanz and Fordow in less than two years, more than doubling its previous enrichment capacity. Reflecting this surge in capacity, Iran’s stockpile of 3.5% or low-enriched uranium has gone from about 2,500kg to around 4,300kg in the same period. In March, Iran announced that it was also building 3,000 of the new, more advanced centrifuges (known as the IR-2m) that are said to be up to five times more efficient than the older IR-1 design. Nearly 700 of the new centrifuges have already been installed. Iran is also making progress with its heavy-water reactor at Arak. Capable of producing plutonium, it could provide an alternative route to a bomb at the end of next year.

Paradoxically, these developments are proceeding without Iran appearing to risk crossing either the red line announced by Barack Obama or the most recent limit set by Israel’s prime minister, Binyamin Netanyahu. Both men have threatened that the consequence of Iran crossing their respective lines would be attacks on Iran’s nuclear infrastructure, but neither line has been drawn clearly. In Israel’s case, the ultimatum set by Mr Netanyahu in September last year was that Iran must be prevented from having enough 20% or medium-enriched uranium (MEU) to allow it to produce the 20 or so kg of HEU required for a nuclear weapon. But how much is that?

More than enough for a bomb

Mr Netanyahu has since suggested that if Iran had 250kg of MEU it would have crossed his red line. But that seems a very high figure for a single nuclear device (see chart). He may have been referring to MEU in the form of uranium hexafluoride that Iran’s enrichment process produces rather than the amount of 20% enriched uranium itself. That is because 250kg of hexafluoride would produce about 165kg of MEU, which is about right for one bomb. Mr Jones reckons the amount of MEU needed for a single bomb could be between 94kg and 210kg depending on how the enrichment to HEU is carried out. Since Iran started producing MEU just over three years ago it has produced 219kg of 20% enriched uranium, of which over 40% has been converted to uranium oxide, some of which has been made into fuel rods for a research reactor in Tehran.

Watch an animated explanation of this diagram here However, that still leaves a 123kg stockpile of MEU, enough for a bomb if Mr Jones is right and therefore already well across Mr Netanyahu’s red line. In the last quarter Iran converted 67% of its MEU production into oxide, but still increased the stockpile by 10kg. Even though Iran is managing its MEU stockpile carefully to keep the negotiations going and preserve ambiguity, on any reckoning it is likely to be well over the line set by Israel before the end of this year. Does that suggest that Israel will carry out a military attack on Iran’s nuclear facilities some time in the next six months? Probably not. Israeli red lines have come and gone in the past. A while ago, Israel wanted it to be thought that Iran would face attack if it gained the capability to build a nuclear weapon. That point was probably passed some years ago. Making a bomb depends on Iran’s ability to convert HEU into a metal sphere for the weapon’s core, to make a reliable detonator and then to create a warhead small enough to put on a ballistic missile, a process known as “weaponisation”. Mastery of the techniques required is not beyond Iran’s engineering capacity. Western intelligence agencies used to reckon that Iran had suspended work on weaponisation in 2004. But after the IAEA published a report in November 2011, since when Iran has refused to allow the agency’s inspectors into the Parchin military research complex facility, that assumption has been challenged. In December 2011 Mr Jones estimated that Iran could produce an implosion-type device within two to six months, thanks in part to the help it is thought to have received from Vyacheslav Danilenko, a former Soviet nuclear weapons designer. North Korea is also believed to have given substantial technical help. Israel subsequently came up with another red line that its then-defence minister, Ehud Barak, called the “zone of immunity”. This referred to the moment when Iran had enough centrifuges in the Fordow facility, which is impregnable to Israeli conventional weapons, to continue enrichment even after an attack. That line was probably crossed a year or more ago.

As Iran’s nuclear programme has advanced, Israel has become less confident of its ability, acting alone, to do more than temporary damage to it. Michael O’Hanlon of the Brookings Institution says that Israel might have attacked three or four years ago, but that it is less likely to do so now. Until last year Mr Netanyahu appeared to hope that if Israel struck first, America would be forced, whatever its initial reservations, to step in and use its greater military resources to finish the job. After being warned unmistakably by Mr Obama that he could not count on any such thing and that America would not be “complicit” in such an attack, Mr Netanyahu came perilously close to trying to influence the presidential election in favour of his friend, the more hawkish Mitt Romney.

Clear enough?

Since then Israel’s prime minister has concentrated on keeping up the pressure on Mr Obama to honour his commitments on Iran. When the president visited Israel in March, both leaders said they shared a “common assessment” of how close Iran was to getting a bomb and were equally determined to prevent it from doing so. Mr Netanyahu said his red line might be crossed before Mr Obama’s and Mr Obama ceded Israel’s right to defend itself as it saw fit. But the reality is that Israel will contemplate a unilateral strike on Iran only if it comes to believe that America has betrayed it by ruling one out. Even then, suggests Mr O’Hanlon, the intention might be to signal to Tehran that Israel “had not gone soft” rather than out of any conviction that it could delay Iran’s progress to a bomb by more than a year or two.

What could prompt Mr Obama to order an attack? In March last year he said that “Iran’s leaders should understand that I do not have a policy of containment; I have a policy to prevent Iran from obtaining a nuclear weapon” and that a “military effort” might be required to divert it from that course. The former defence secretary, Leon Panetta, went further, saying that if America received intelligence that Iran was “proceeding with developing a nuclear weapon” or that a decision had been taken to that end, America would “take the necessary action to stop [it]”. Moreover, the Obama administration has repeatedly claimed that it would know when such a decision had been taken and would have time to respond. So, not much ambiguity there, then? Well, actually, quite a lot.

Mr Obama’s red line rests on at least three questionable assumptions. The first is that the evidence that Iran has taken the political decision to become a nuclear weapons state will be sufficiently compelling to allow for no other interpretation. The second is that there will be a significant interval between such evidence presenting itself and Iran actually having a weapon that it might be willing to use to deter an attack. The third is that a strike or series of strikes bringing America’s military might to bear on Iran’s nuclear facilities would achieve its aims.

Mr O’Hanlon believes that Mr Obama is “locked in” to taking military action if Iran signals its intentions, for example by renouncing the Non-Proliferation Treaty and throwing out the IAEA’s inspectors. Kenneth Pollack, of the Saban Centre for Middle East Policy at Brookings and author of “Unthinkable: Iran, the Bomb, and American Strategy” (to be published in September), is less convinced that the “US will get a clean shot” of that kind. If Iran left the NPT, it would say it was doing so because it regards the agency’s inspectors as spies, not because it wants a nuclear weapon. Moreover, he believes that Mr Obama will demand a very high standard of proof following the intelligence debacle over Iraq’s weapons of mass destruction.

Take my hand and stop worrying The idea that there will be plenty of time between Iran making the decision to build nuclear weapons and actually getting them is a comforting conceit that Western intelligence agencies have clung to. The implication is that there will be opportunities for careful alliance-building and diplomatic ultimatums before any strike has to take place. But with Iran approaching critical capability that may not be true. As time goes on, the period that Iran needs to produce not one or two but several devices undetected shrinks, increasing the chances of Iran being treated in much the same way as other aspirant nuclear states that have crossed the threshold, such as Pakistan and North Korea. The third questionable assumption is that air strikes on Iran’s nuclear facilities would achieve their objective. If Iran, after leaving the NPT, had stockpiled sufficient MEU for several bombs and hidden it well, the chances of finding and destroying it would be small. It could decide to absorb an attack and then, using a still largely intact Fordow or a clandestine plant, move quickly to fissile material production.

No good options

Mr Obama may well conclude that if his military planners cannot be confident of delaying Iran’s progress to nuclear weapons for a long time—at least five to ten years—or changing Iranian behaviour, it is not worth trying. Just as troubling, if bombing was tried and it failed, Mr Pollack thinks Mr Obama would have to follow up with a full-scale invasion. “No American president would or could say, we gave it our best shot, but we can’t finish the job,” he says. Mr Jones has similar fears. He says that such is the scale of the country’s centrifuge enrichment programme that a prolonged bombing campaign would be required to halt it and that “would run a serious risk of turning into a large-scale war with Iran”. America could hammer Iran, but having brought American forces home from Iraq and Afghanistan this is the last thing that Mr Obama wants for his war-weary, financially drained country.

Anthony Cordesman, of the Centre for Strategic and International Studies in Washington, DC says that one choice is containment and the other military strikes—followed by containment. Given that sanctions and diplomacy are unlikely to alter Iran’s course and that force will not achieve a lasting solution, he thinks America and its allies must start thinking through what containment and deterrence of a nuclear Iran will require.

What nobody knows, quite possibly not even the supreme leader himself, is when and how Iran will step across the nuclear threshold. Pakistan waited nearly 12 years between acquiring enough fissile material for a bomb in 1986 and carrying out a succession of nuclear tests in 1998. Iran might be similarly patient, a course Mr Rohani may advocate. On the other hand, if he fails to win softer sanctions Iran could try to bring things to a head more quickly. What is increasingly hard to believe is that it can be dissuaded or prevented from getting the bomb by force. The challenge for Western policymakers may be less about stopping Iran than managing the consequences of it having a nuclear weapon, which include the unravelling of the entire non-proliferation system.