Nuclear negotiations between Iran and the P5+1 powers — the United States, Britain, France, Germany, Russia, and China — resume this week in an atmosphere that is at once hopeful and grave. Officials from both sides have been surprisingly optimistic about their chances of reaching a long-term accord. Yet serious differences reportedly remain, and failure to resolve them would leave both sides to weigh the unpalatable alternatives to a diplomatic resolution.

Failure would be easy to recognize; what success would look like is less clear. Despite U.S. officials’ insistence that “no deal is better than a bad deal,” they are also keenly aware that promising diplomatic openings with Iran have been few and far between in the past 35 years, and likely worry that Iranian President Hassan Rouhani’s ability to withstand domestic opposition to his economic and diplomatic initiatives may be fleeting.

Rouhani’s purported weakness is paradoxically a source of Iranian advantage in these negotiations. While no political reformer, he is widely perceived as someone who is serious about resolving the nuclear dispute so that Iran can recover economically. U.S. and European observers hope that a nuclear deal could lead to a broader easing of tensions — though whether this is true is unclear — and conversely worry that failure to reach a deal could fatally undermine that chance.

Rouhani has correspondingly engendered sympathy for his constraints. Indeed, a “good deal” these days is often framed more in terms of Rouhani’s capacity to deliver than our own requirements. Issues such as Syria and Iran’s missile programs are often dismissed by observers as off the table because they are in the purview not of Rouhani but of the Revolutionary Guards, implying that we are negotiating not with the Iranian regime but merely one faction of it. But softening our nuclear demands in the hope of strengthening Rouhani would be a mistake, for several reasons.

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