LONDON — The spin masters are out trying to portray the failure of Iran talks in Geneva this way or that. It was the French who abruptly got tough. No, it was Iran’s insistence that its right to enrich uranium be acknowledged. No, it was just the formidable difficulty of a negotiation between mistrustful adversaries.

In this mess, with its bitter aftertaste, it is worth returning to basics. First, President Hassan Rouhani, the Iranian president, and Mohammad Javad Zarif, Iran’s foreign minister, represent the most serious, credible, moderate and capable negotiators the Islamic Republic is ever likely to produce. There will not be a better opportunity with any other conceivable team within a useful time frame.

Second, according to people who have spent many hours with them, Rouhani and Zarif are prepared to limit enrichment to 3.5 percent (well short of weapons grade); curtail the number of centrifuges and facilities and place them under enhanced international monitoring; deal with Iran’s 20 percent enriched stockpile by converting it under international supervision into fuel pads for the Tehran research reactor; and find a solution on the heavy-water plant it is building at Arak that could produce plutonium. In return, as these steps are progressively taken, they want sanctions relief and recognition of the right to enrichment.

Third, although Western intelligence agencies believe the Islamic Republic has not taken the decision to make a bomb, Iran’s nuclear program has advanced far enough for the country to have the relevant knowledge. Destroying this know-how is near impossible. Iran knows how to produce weapons-grade fissile material; it may not yet be able to make a deliverable weapon. So, as Stephen Heintz, the president of the Rockefeller Brothers Fund, put it to me, “The key for the international community is to put all that capability in a box where it is verifiable, contained and controlled. That is what the deal is about.”Fourth, Iranian sanctions weariness on the one hand and U.S. Middle Eastern war weariness on the other have produced a rare moment of mutual interest in exploring openings that might overcome or mitigate decades of hostility that now serve the interests of neither power. Given the powerful forces arrayed against a deal — from Israel to Congress by way of Saudi Arabia and Iranian hard-liners — such readiness is likely to be fleeting.

Fifth, Israel has denounced a possible interim deal with Iran. Benjamin Netanyahu, the Israeli prime minister, warned American Jewish leaders Sunday that an Iranian nuclear weapon is “coming to a theater near you.” But all this hyperbole — Secretary of State John Kerry has referred to “fear tactics” — cannot mask the fact that, absent an agreement, Israel faces the scenario least in its strategic interest: Iranian centrifuges still spinning, the United States still war averse, with the possibility of having to go it alone in a military strike that might dent but would not stop Iran’s nuclear ambitions and would without doubt ignite regional turmoil.

All this speaks for the critical importance of seizing the moment and clinching an exacting interim deal that gets all that Iranian nuclear capacity in a verifiable box and builds the confidence needed for a broader accord.

A word on France: Its position reflects strong views on nonproliferation, its defense agreement with the United Arab Emirates, and a mistrust of the Islamic Republic that runs deep. There are good reasons for this mistrust. Laurent Fabius, now the foreign minister, was prime minister in the mid-1980s during a wave of Paris bombings that were linked to pro-Palestinian groups but are also believed by French authorities to have had Iranian backing in several instances. Fabius is not about to forget this or cut Rouhani any slack. This is not a bad thing. A deal has to be watertight in blocking Iran’s path to nuclear weapons while acknowledging its right to nuclear energy.

Which brings me to Iran’s right to enrich. Iran is a signatory of the nuclear Non-Proliferation Treaty. This refers to “the inalienable right of all the Parties to the Treaty to develop research, production and use of nuclear energy for peaceful purposes.” Many non-nuclear countries, including Germany and Japan and Brazil, have interpreted this as a right to enrich uranium — and they have done so with the agreement of the international community. The United States does not see in the treaty language an inherent “right to enrich,” but President Obama has said, “We respect the right of the Iranian people to access peaceful nuclear energy in the context of Iran meeting its obligations.”For a country like Iran that has threatened Israel with destruction and engaged in international terrorism, the bar must be much higher on the right to low-level, highly monitored, peaceful enrichment. But it is an inescapable and legitimate component of any conceivable deal that would usher Iran into the family of nations — which is where the United States and Israel have common interest in seeing it.