The Iranian nuclear deal appears to have been unable to put one key issue fully to rest, leaving it to be worked out in practice despite the risk it could severely test the agreement's viability.
That is the thorny problem of how much spontaneous access international inspectors monitoring the deal will have to Iranian facilities where nuclear activities take place.
Some of those facilities are military bases and throughout the negotiations Tehran resisted demands that inspectors from the UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), should have the right to make unannounced visits to any site where they know or suspect nuclear activities are taking place.
The best Iran would offer, after an initial refusal by Supreme Leader Ali Khamenei on May 20 of any inspections of military sites, was what Tehran termed "managed access." Iranian Deputy Foreign Minister Abbas Araghchi told the press that could mean blindfolding inspectors or covering up equipment to ensure they did not see anything that might betray Iranian military secrets. An Iranian lawmaker said it would mean limiting inspectors to taking environmental samples around military facilities.
However, such restrictions were promptly rejected by Washington. U.S. Deputy Secretary of State Antony Blinken said on June 8 that the United States would not accept a deal unless access was granted "to whatever Iranian sites are required to verify that Iran’s program is exclusively peaceful -- period."
With the two sides initially so far apart, the Vienna negotiators had to search hard for a compromise and, in the end, appear to have found one that defers the hard work of actually deciding how much access inspectors have to a later time.
News agencies report that Iran and the six powers -- the United States, Russia, China, Britain, France, and Germany -- agreed to allow UN inspectors to request visits to military sites but that Tehran would have the right to challenge the IAEA requests. In the case of a disagreement, the issue would go to an arbitration board composed of Iran and the six powers for a decision.
However, that case-by-case approach could risk satisfying neither side in the event of serious disputes. It could also fuel criticism of the Vienna deal among its opponents in both Washington and Tehran who see their governments as conceding too much at the negotiating table.
Critics of the deal in the West are likely to argue that the very process of referring requests for inspections of military sites to an arbitration board offers Iran a window for removing evidence of suspected nuclear activities before visits can take place.
Similarly, hard-liners in Tehran, who have resisted negotiations with the six powers throughout, may argue that the deal endangers national security by giving ultimate authority over which sites inspectors visit to an arbitration board that includes the United States, which Iran regards as a hostile power.
Officials on both sides sought to neutralize these concerns by getting the deal off to a flying start immediately after it was announced on July 13.
Iranian Foreign Minister Mohammad Javad Zarif welcomed the deal as an "historic" agreement and a "win-win" solution to the dispute over Iran's nuclear program. U.S. President Barack Obama called the deal an opportunity to move in a new direction and that "we should seize it."
But with the prospect of potentially tough case-by-case negotiations looming in the future, the real tests of the agreement's strength and its staying power may still lie very much ahead.