After 12 years of bitter accusations, threats of war, escalating sanctions, and interminable diplomacy, nuclear talks with Iran appear to be entering the final strait.

Last November, six world powers and Iran agreed a so-called Joint Plan of Action (JPOA). This committed Iran to freezing much of its nuclear activity - including the especially sensitive enrichment of uranium to 20 percent - in exchange for limited sanctions relief from the West. That deal expired on November 24. Although diplomats are free to keep talking after that date, the problem is that neither side will any longer be bound by these constraints. Iran will be free to resume higher-level enrichment, and the United States to impose fresh sanctions. Lawmakers and hawks in both capitals will agitate for their governments to do precisely this, even if Presidents Barack Obama and Hassan Rouhani want more time. That would take us back to the confrontational and tense atmosphere of 2012 and 2013, where the spectre of military action cast a dark shadow.

While diplomats acknowledge that great progress has been made in the past year - more than in the previous decade put together - there reportedly remain crucial gaps, specifically over the amount of enrichment that Iran will be permitted to undertake, how long Iran will be bound by any restrictions, and the sequence of sanctions relief.

An extension?



Most therefore predict that negotiators will seek an extension of a few months, and perhaps even a "framework agreement" that pins down the areas of consensus. If this is the path chosen, they should know that they would face a rapidly closing window for dialogue, one that might snap shut by spring 2015 at the latest. Although Obama would theoretically be able to veto Congress' attempts at new sanctions, it is less clear whether Iran's Supreme Leader would give Rouhani the latitude to keep the nuclear programme frozen.

As for the content of a deal, the two sides are within touching distance. Consider one crucial aspect. Currently, Iran could produce enough fissile material for one nuclear bomb - although not the bomb itself - in less than two months, a scenario known as "breakout". The West wants to extend this to at least a year. As part of any deal, Russia seems likely to ship out Iran's stockpile of enriched uranium to create fuel rods. This helps, but even if we assume Iran starts with no enriched uranium, it would still have to cut its number of first-generation centrifuges down to just over 5,000 if the breakout time is to stretch to a year. Iran currently has 18,000 (8,000 are inactive, but this doesn't matter for these calculations). According to press reports, the highest reported US offer is 4,500 and the lowest reported Iranian one is 8,000.

These details sound arcane, but the takeaway is simple: the devil really isn't in the detail. Even if we crudely split the difference, and assume a 6,000-centrifuge compromise, then we still end up with a 10-month breakout time. Iranian breakout would be detected within days, leaving ample time for a diplomatic and military response.

Israel's insistence that this would leave Iran at the "nuclear threshold" is simply not credible. And it is hard to understand why an extra two months would make much difference - and equally important to remember that an obsession with centrifuge numbers can come at the expense of attention to covert routes to the bomb, which can only be closed off through broad, intrusive inspections.

Politically toxic step

The real challenge here is that Iran must commit to the politically toxic step of dismantling thousands of its machines, because merely disconnecting some piping, or locking them in a cupboard, doesn't really buy you much time. But even if we had allowed Iran to keep all its operating centrifuges, this problem would still have come up, given its plethora of inactive but installed machines. It's up to Iran whether it chooses to emphasise the dismantling, or the fact that it gets to keep thousands of centrifuges - this will shape whether it can sell a deal at home.

Centrifuges aside, the issue of sanctions relief is proving to be particularly thorny. The US is offering the release of blocked funds and temporary sanctions waivers, with more permanent sanctions relief - requiring the approval of an intransigent Congress - further down the line.

Iran is understandably wary of limited and reversible measures, not least because the economic benefits are one of its primary motives for negotiating a deal in the first place. But assuming that these and other differences are bridged, what will be its regional implications?

A deal is not the same thing as rapprochement. The US' regional allies - Gulf states, Israel, and Turkey - all fear that a deal might prompt further US-Iran alignment at their expense. A letter from Obama to Ayatollah Khamenei, reportedly implying that a deal would enable cooperation against ISIL, as well as Obama's explicit admission that he wants a "political conversation" on Syria to include Iran. Last month, the US envoy to the anti-ISIL coalition acknowledged that "we have welcomed Iran's constructive role in Iraq", and "we are going to continue to listen very carefully to the things they have to say".

At the same time, Obama knows that sudden, overt collaboration with Iran would cause Arab allies to peel away from his military coalition in Syria, and complicate efforts to stand up armed Sunni forces in ISIL-afflicted parts of Iraq. Moreover, any meaningful US-Iran dialogue is premised on the US talking directly to Iran's Revolutionary Guards, who oversee Iran's extensive interventions in Syria and Iraq, or the Supreme Leader handing over the portfolio to Iran's more pragmatic foreign ministry. Neither scenario seems especially likely, and so the idea of US-Iran cooperation - whether one fears of welcomes it - is likely to outstrip the reality, in the months after any deal.

The reverse, however, is more worrying: if diplomacy collapses, the negotiating window slides shut, and Iran's nuclear programme starts re-expanding, the prospect of an Israeli or US war comes back into the picture, except this time both Tehran and Washington are already committed to open-ended campaigns, on multiple fronts, and, in Iraq, against the same adversary.

Shashank Joshi is a research fellow of the Royal United Services Institute in London and a PhD candidate at Harvard University. He holds Masters degrees from Cambridge and Harvard universities. He specialises in the international politics of South Asia and the Middle East.