The meetings in the gilded rooms of Lausanne between Iran, the United States and its diplomatic partners went beyond an artificially imposed deadline on Tuesday night. There was growing optimism that negotiations in the Swiss town would yield a tentative agreement over Tehran's controversial nuclear program.
In any event, no final deal will be concluded until the summer, at the earliest. Here's a guide to the big, tough questions that would surround any lasting agreement with Iran.
What's the plan to prevent an Iranian nuclear weapon?
Iran, a signatory to the United Nations' Non-Proliferation Treaty, insists that it has no intention of building a nuclear bomb. Those claims are viewed with skepticism by officials in Washington and elsewhere. Hence, the many rounds of both sanctions and talks in recent years.
The United States and its partners want to extend as long as possible the potential "breakout time" -- the time it would take for Iran to produce enough highly enriched uranium to make one atomic bomb, should Tehran go down that route. Current estimates place that time at around three months. The negotiations in Lausanne are expected to yield a framework that would shift it to about a year.
This would be accomplished through a number of measures: imposing an even tighter regime of international inspections than that already in place; capping the number of centrifuges -- the whirling devices that enrich uranium into potentially fissile material -- Iran has installed; and placing tighter controls over Iran's enriched-uranium stockpiles.
It appears the United States and Iran have settled on limiting Tehran to 6,000 centrifuges (it has more than double that now in two sites); hawkish critics of the Obama administration, including Israeli Prime Minister Benjamin Netanyahu, want to see that number reduced to zero. That is a diplomatic nonstarter for the Iranians, who take a lot of pride in their nuclear program and contend it's needed for civilian purposes. A more measured approach would be to limit Iran's ability to upgrade its largely outdated centrifuges.
One potential arrangement being discussed would involve Iran shipping a chunk of its enriched-uranium stockpile to an outside country, such as Russia. This appears to be an unfavorable option for the Iranians, who would rather keep their uranium at home and dilute it to acceptable levels, as they have already done since an earlier interim agreement in 2013.
Is this really just a numbers game?
No, not at all. Even the basic technical matters that frame the negotiations are subjects of endless debate. Hawks offer more narrow calculations of Iran's potential "breakout time," warning that Iran's pathway to a bomb would not be as impeded as the White House thinks. Other analysts, meanwhile, say the whole issue of breakout is a red herring: that, if Iran chose to build a bomb, it would do so clandestinely -- and not through facilities already extensively monitored by international inspectors.
That raises the thornier question of whether Iran would actually take the giant political risk of building a bomb. Iran has had the theoretical capacity to do so for some time now, yet it has chosen not to. Some experts also reckon the United States would be able to successfully contain or deter Iran, even if it had a nuclear weapon.
Underlying the negotiations over Iran's nuclear program are other greater geopolitical concerns. These include the fears of Iran's regional rivals -- including Israel and Persian Gulf Arab states such as Saudi Arabia -- over Tehran's supposed ambitions to be a Middle Eastern hegemon. Iran, meanwhile, looks at the past decade and a half of American wars in Iraq and Afghanistan and sees its own encirclement by a longstanding foe.
For proponents of rapprochement between the United States and the Islamic Republic, agreements over centrifuges and uranium stockpiles are ultimately small, confidence-building steps toward a larger reconciliation. Patching up more than three decades of enmity is no easy task.
How long can a deal last?
Crucial to any agreement is the time-frame of a potential final deal. Reports indicate American negotiators are seeking a 10-to-15-year window during which the sanctions stifling Iran's economy would be gradually eased in return for Iranian compliance and cooperation. Iran desperately needs this relief to kick-start its economy.
But there are differences over how soon some of these sanctions would be lifted -- the Iranians obviously want more immediate concessions -- and what measures would be in place should Iran be found to be violating the terms of any final deal. It is difficult to efficiently reimpose a whole regime of sanctions once they have been dismantled. Some in the West are loath to lose their economic leverage over Tehran.
The wrangling over this complex stage of the negotiations has exposed disagreements not just between Iran and its interlocutors, but the United States and other members of the P5+1 (the five permanent member states of the U.N. Security Council plus Germany) participating in the talks. Russia, for example, is wary of any mechanism that would automatically trigger sanctions on Iran without passing the Security Council, where Russia and the other permanent members wield veto powers.
How will it play back home?
Parallel to all the summitry in the manicured environs of Swiss hotels are heated, sometimes silly domestic conversations both in the United States and Iran.
Despite polls suggesting a clear majority of Americans want to see diplomacy succeed with Iran, the issue has become a partisan rallying cry in Washington, highlighted by a controversial speech delivered by Israel's Netanyahu and a controversial letter to Iran signed by 47 Republican senators.
The White House wanted to have a framework of a deal in place this week in order to strengthen support ahead of a mid-April battle in Congress, where a new Senate bill could derail the talks and lead the way for more U.S. sanctions on Iran.
Meanwhile, Iranian President Hassan Rouhani and Foreign Minister Mohammed Javad Zarif are contending with hard-liners in Iran, who criticize the current leadership for trusting their American interlocutors and accuse it of being cowed and bullied by Western demands. Narratives of national humiliation and wounded pride are ingrained in the Iranian political discourse.
Lurking behind all this, of course, is Iran's supreme leader, Ayatollah Ali Khamenei. The fate of the whole process, some argue, hinges on whether the aging ayatollah will be able to accept all the concessions Iran must make.