The word “breakthrough” has been uttered hopefully in anticipation of the meeting May 23 in Baghdad of officials from six world powers and Iran to resolve the standoff over Iran’s nuclear program. A positive meeting last month in Istanbul kindled a sense of momentum.

The U.S., which has kept the talks on track as Iran has tried to wiggle out of them, wants Iran to freeze its program and agree to future negotiations on capping uranium enrichment and opening nuclear sites to full international inspection. But success will continue to rely on the unified U.S., European, Russian and Chinese decision to impose punishing economic sanctions on Iran, and that cohesion is now under threat.

It’s shaky not just because Russia and China are, as usual, difficult to keep in the corral. The new and greater challenge is the risk that the just-elected French president will break ranks and that economic woes will lead to a further dissolution of European resolve to confront Iran’s nuclear program.

Before Nicolas Sarkozy became president in 2007, France, like the rest of Europe, took a softer approach to Iran than the U.S. But Sarkozy was hawkish on Iran, and eager to move France closer to the U.S. He argued for robust international sanctions to compel Iran to give up its presumed nuclear weapons program. His approach influenced the U.K., and eventually hardened the position of the rest of Europe. Under Sarkozy, France led Europe in insisting on a tightening of financial pressure and a European embargo on Iranian oil, set to begin July 1.

France’s new Socialist president, Francois Hollande, is distancing himself from Sarkozy’s legacy, including on the Iran policy. Shortly after Hollande’s victory, former Socialist Prime Minister Michel Rocard visited Iran on a private but symbolic trip. Although Hollande has publicly pronounced his support for the U.S. position, it was clear from the comments of Iranian officials who met with Rocard that they are confident France will no longer serve as the hard line at the negotiating table.

Continuing economic troubles pose another challenge to European unity on Iran. The boycott of Iranian oil may lead to higher energy prices in Europe, which could prove unpopular, especially on top of austerity measures that are already emboldening the populist left across the region. Iran might pursue the strategy it has adopted with China and offer struggling European economies oil at discount prices. Confronting Iran may no longer be a European priority in the face of the region’s grave financial problems.

If Europe slides, it would be difficult for the U.S. to keep China and Russia in the fold, especially with both sets of relations recently tested. A cloud hangs over U.S.-China ties after the diplomatic tussle over dissident Chen Guangcheng, who sought refuge in the U.S. Embassy in Beijing. As Iran’s largest trading partner, China has significant control over whether the sanctions regime works. Only recently has China begun to enforce sanctions, cutting its Iranian oil imports by 11 percent. It can do much more to curtail Iranian financial transactions and trade.

Russia has always balanced its strategic relationship with Iran with keeping the U.S. content. The “reset” of U.S.-Russia relations during the Obama administration’s first year tilted that balance in Washington’s favor. But there is growing suspicion of U.S. intentions in Russia and a willingness to score political points by feeding anti-Americanism. Thus the Kremlin is in no mood to do the U.S. any favors on Iran and instead prefers obduracy.

To Iran, this is all welcome news: The international alliance against its nuclear program is losing focus and may unravel. Almost certainly, there will be no further sanctions, and those on the books will be implemented inconsistently. Such a reading will probably lead Iran to take a confident, uncompromising position in the nuclear negotiations.

The challenge, then, is to keep intact the international alliance that was created to prevent just that. The U.S. should work harder at mending fences with Russia and China to keep them onboard. And European officials should exercise leadership in keeping this crucial security matter on their agenda. Otherwise, Iran will have no reason to resolve the nuclear issue. Far from a breakthrough, what we can expect from the nuclear talks in that case is a long, slow and frustrating process.

(Vali Nasr is a Bloomberg View contributor, a professor of international politics at the Fletcher School of Law and Diplomacy at Tufts University and a senior fellow in foreign policy at the Brookings Institution. The opinions expressed are his own.)

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To contact the writer of this article: Vali Nasr at vali.nasr@tufts.edu.

To contact the editor responsible for this article: Lisa Beyer at lbeyer3@bloomberg.net.