First, if Iran were discovered to have built, or be building, a hidden enrichment facility, this would likely trigger a military response from the U.S. This is not an implausible scenario: Iran has already built two secret nuclear facilities — subsequently discovered by Iranian dissidents and by the West — at Natanz and at Fordow. The discovery of these facilities led to heightened sanctions, but not to military action.

At this late stage, though, particularly when Iran has promised to negotiate in good faith, the discovery of a third such facility would prove once and for all that the regime is intent on sneaking across the nuclear finish line and would most likely force an Obama response. I don’t think it’s probable that Iran is building a large-scale secret uranium enrichment facility inside a mountain, as it succeeded in doing at the Fordow site, near Qom. The regime understands that the discovery of a facility could be catastrophic. But it’s within the realm of possibility.

Second, like Gary Samore, Obama’s former Iran nuclear specialist, I think it is more likely that the regime would try to sneak across the finish line than make an overt dash for it. An overt dash would mean the expulsion of international weapons inspectors and a fairly obvious push to enrich uranium to weapons-grade levels. Iran, at this moment, could do this in a fairly short period of time, but I think initiating this dash would also trigger an immediate Obama response.

Obama will probably not face either of these scenarios.