Iran was mentioned early and often in last night's third and final presidential debate—47 times, more than any other foreign country. But for all that chatter, neither Barack Obama nor Mitt Romney got into the most salient details about the standoff with Iran over its nuclear program: what kind of deal would be required to avert the war both candidates said would be a last resort—never mind that an attack might not work.

Though Obama did mention that Iran could "regain credibility," he said the "deal to be had" with Iran was that they "convince the international community they are not pursuing a nuclear program"—that is, not a nuclear weapons program, but a nuclear program, fullstop. Iran, however, will insist on maintaining a program of some sort in any final compromise. Romney, whose campaign has in the past backed the non-starter of "zero enrichment" for Iran, said the U.S. should "dissuade Iran from having a nuclear weapon through peaceful and diplomatic means." But the specifics sounded like Obama. "[A]n Iranian nuclear program is not acceptable to us," Romney said. "They must not develop nuclear capability."

The "capability" line—one I wish Bob Schieffer had asked about—makes for one minor distinction between the candidates. Nuclear weapons capability is ill-defined but, as a trigger for action, clearly sets a lower threshold for war than where Obama sets his "red line," at nuclear weapons production. Another distinction, reinforcing Romney's skepticism about a deal, was the former Massachusetts governor's pledge to further isolate the Iranians. "I would also make sure that their diplomats are treated like the pariah they are around the world," he said. The question then remains: how do you make a deal with a country whose diplomats you have just made pariahs?

This seems to be a central point bedeviling whatever macabre dance the U.S. is engaged in with Iran. Those with a hawkish bent tend to insist sanctions haven't worked. But sanctions cannot work, so to speak, until the pressure they exert yields a mutually agreeable deal. Make no mistake: the sanctions are inflicting pain on Iranians, as evinced by the fact that, in Obama's words last night, "their economy is in a shambles." But when will new sanctions end and the diplomatic dealmaking begin?

The last days of a presidential debate are probably not the time for Presidents and would-be Presidents to make foreign policy. But Iranian leaders have been preparing their population for a deal—making the dubious claim that they only want a peaceful program and issuing fatwas to that effect, allowing them to save face by saying they got what they always wanted: recognition of their nuclear rights. It is our American leaders who paradoxically have not spoken to their people at all about the contours of a realistic compromise. If Romney and Obama were serious when they alluded to the clock running down on Iran, they'd better start explaining just how sanctions can finally work by offering a deal the Iranians can take.