With the first round of nuclear talks with Iran's new, and newly pragmatic, negotiating team in the books, the Washington policy debate about Iran has shifted from whether a deal is possible to what sort of deal is acceptable. While such discussions can often seem a miasma of centrifuge counts and enrichment levels, there are, in fact, two distinct paths to a nuclear deal with Iran.
The first path is one in which Tehran would receive relief from sanctions in exchange for putting strict limits on its nuclear activities, such as restricting uranium enrichment to low levels. The success of such an agreement would depend on ensuring that Iran could not use declared nuclear activities as a cover for covert activities aimed at developing a nuclear weapon. It would also depend on ensuring that the deal was not easily reversible, so Tehran could not renege once pressure had been alleviated.
There are ways that sanctions relief could be made more easily reversible — for example, channeling oil payments to Tehran through a single mechanism that could be blocked in the event of noncompliance — but none of these is fail-safe. The efficacy and durability of a deal over limited enrichment would rest on Iranian transparency. To be meaningful, transparency measures would have to include allowing inspectors unfettered access to sites of their choosing, not just those declared by Iranian officials, and a comprehensive accounting of Iran's past and present nuclear work, including the military elements of its nuclear program, such as weaponization research.