Reuters The French balked at a deal with Iran over concerns about the Arak plutonium reactor, which may give Tehran a quicker path to nuclear weapons than enriched uranium.

In the end, John Kerry put it best. "It takes time to build confidence between countries that have really been at odds with each other for a long time now," said the U.S. Secretary of State. A deal between the West and Iran over its nuclear program is still possible--talks resume on Nov. 20--but the breakdown of talks in Geneva made a tough challenge even more difficult.

In diplomacy, transparency is often the enemy of progress. Negotiations are best conducted secretly until there is an agreement. When carried out in full public view, the process simply allows opponents to attack every concession made to one side, paying little attention to the concessions to the other. Even imagined concessions get attacked. Israeli Prime Minister Benjamin Netanyahu furiously protested against the proposed deal with Iran even though, as Kerry suggested, he didn't actually know what was in it. Ironically, it is to prevent just this problem that Netanyahu has insisted that talks between Israel and the Palestinians take place in strict secrecy.

One party that did know what was in the proposed agreement was France. The French took the unusual step of breaking ranks with their Western colleagues to publicly denounce the deal on the table. This has led some to wonder whether France's strategy was to demonstrate its hard-line credentials to the most anti-Iranian states in the Middle East--Saudi Arabia, in particular--and thus gain favor. (Paris has signed a multibillion-dollar defense deal with Riyadh in recent months.) And of course, being anti-American comes naturally to a French President, especially one from the Socialist Party, like François Hollande.

But whatever France's motives, its concerns have merit. They seem to center on Iran's nuclear reactor in Arak, which is under construction and if completed would produce plutonium rather than uranium. If one fears that Iran is seeking a path to nuclear weapons and not just nuclear energy, a plutonium reactor is a red flag. It could easily produce enough weapons-grade plutonium for one or two bombs every year. And once fully operational, it is largely invulnerable because a military strike against it would release radioactive toxins into the atmosphere. Thus the West has demanded that Iran stop work on this reactor, and this appears to have been one of the key points of disagreement in Geneva.

There are solutions. The danger of an operational plutonium reactor is not immediate. Iran is well behind schedule on the Arak facility. Olli Heinonen, former deputy director of the International Atomic Energy Agency, has recently suggested that the reactor would be able to generate usable plutonium only in 2016. Remember, the deal proposed in Geneva allowed Arak to continue functioning but only for six months, during which time both sides were going to try to negotiate a final and comprehensive deal. If that fell apart, in the spring of 2014, Arak would still be nonoperational.

While France's objections can be assuaged, those of some of the other opponents cannot. Netanyahu wants Iran to have no enrichment capacity at all; that, for Iran, is a "red line." It's not entirely clear whether Netanyahu's demand is a bargaining position or whether he will denounce any deal that allows the Iranians to enrich uranium.