On Tuesday, opponents of the Iran deal made their (apparently last-ditch) cases at D.C.’s premier think tanks. At Brookings, John McCain led the anti-deal side in an expert debate, and at the American Enterprise Institute, Dick Cheney lambasted the agreement before one of the few remaining audiences that will listen to him. Cheney’s speech seemed to effectively concede President Obama’s argument that the alternative to a deal is war. After laying out a far-fetched “alternative” which amounted to maximum Iranian concessions on practically every point of contention, Cheney declared that if Iran rejected such an offer, the U.S. should prepare to attack. During his appearance at Brookings, McCain was a bit less theatrical, but he did express concern that diplomacy was lending legitimacy to Iran’s leadership. As Shadi Hamid noted, the debate seemed to turn on precisely this issue.

What #BrookingsDebate makes clear is that opposition to Iran deal isn't actually abt the Iran deal: it's abt the nature of Iran's regime.

— Shadi Hamid (@shadihamid) September 8, 2015

In the Foreign Affairs essay I wrote about last month, Gideon Rose suggested that in retrospect, Obama’s cool treatment of Iran’s 2009 “Green movement” seems to have been based in two strategic judgments. First, as Rose writes, Obama determined that the regime was not in danger of collapsing, and so U.S. support of the opposition would have been futile. (Even under better circumstances, American support probably would have been counterproductive.) Second, as Rose suggests, Obama was probably prioritizing the nuclear deal over other Iran-related issues. Obama’s much-criticized reluctance to extend further support to the Green movement likely bought credibility for the U.S. during nuclear talks.

If that reading of history is correct, it suggests that the position of moderate elements within the Iranian leadership is strengthened vis-à-vis hardliners when the U.S. backs off from openly contemplating war or regime change. The hardliners’ relative aggression is most compelling when it seems closest to reality—when the United States is at its most bellicose. Conversely, a cautiously extended American hand weakens hardliners by making their hostility seem less well-founded. The shape of Iranian opinion seems to confirm this dynamic: as Hamid also noted, Iranian democrats do indeed back the deal.

Critical pt from @MaloneySuzanne at #BrookingsDebate: Most of Iran's democrats support the deal and they know their context better than us.

— Shadi Hamid (@shadihamid) September 8, 2015

This argument is given more support by USC’s Matthew Gratias, who argues in a Scholars Strategy Network policy brief that rather than cowing Iran’s leadership, military strikes would likely empower its radical faction. “Since 1997,” Gratias notes, “the central Iranian political conflict has unfolded between reformist elites who want to lead the country into a post-revolutionary period and reactionary elites who want Iran to forever remain a revolutionary state.” American military attacks would cripple the reformers and “reignite the revolutionary fervor of the clerical elite and Islamic Revolutionary Guard Corps.” U.S. strikes, by uniting Iranian leaders under a common threat, would “eliminate one perennial source of elite political divisions of the kind that have given moderates a beachhead.”

Fortunately, with the exception of Cheney family, there’s little appetite among Americans for another attempt at regime change by force, since such an effort would undermine what might be already be underway. Iran is a young country: more than half of its population is under 35. This group remembers 2009, but not 1979, and a diplomatic agreement averting war could help undermine the hostilities that have historically underpinned official regime ideology. It is true, as critics have noted, that the deal’s most stringent limits last for only 15 years. But Iranian politics are shifting, and the success of the agreement over the next decade-plus could buy important time. At the Brookings debate, McCain worried that striking a deal with Iran’s leaders would simply lend them legitimacy. But absent a disastrous war, the regime isn’t about to crumble. The more intriguing possibility is that the deal might end up lending badly-needed time and credibility to reformers.