How can Iran be stopped from producing nuclear weapons? Debate over this vital issue casts those favoring diplomacy and sanctions against others who insist that sanctions will not 'work', and therefore a preventive military strike is the only alternative. The problem is that both sides are wrong. Neither sanctions nor force will 'work' in this case.

The current regime in Iran is determined to achieve the capability to make nuclear weapons. It would prefer to avoid sanctions and political isolation, and will charade minimal cooperation to avoid them. But it is unlikely to abandon its pursuit even in the face of sanctions that impose real costs.

Unfortunately the use of force will not 'work' either. The U.S. can certainly bring considerable force to bear against Iran. However, accomplishing military strikes and achieving the political objectives for which force was deployed are two different things. A military strike by the U.S. on Iran will almost certainly fail to achieve its political objective: reducing the possibility that the current, unsavory regime in Iran will acquire nuclear weapons. If anything, such a strike would make that alarming outcome more likely.

Consider Iran: a country the size of Alaska, very mountainous, with a population of over sixty-five million people. A common scenario for a preventive U.S. airstrike is a thirty day, round the clock air campaign. After that bloody month, what will the U.S. have achieved?

On the positive side will be the reduction in Iran's potential nuclear capability. But to what extent will Iran's nuclear program be degraded? That is, by how many months or years will its nuclear program be set back? The answer depends on the quality of U.S. intelligence, and also, crucially, on whether Iran has anticipated that such an attack might take place, and has thus hidden, hardened, and dispersed its nuclear activities. It is inconceivable that Iran has not anticipated the possibility of a U.S. strike.

Against those months of delay gained are formidable negatives. What will be the effect of this large military campaign on regional politics? (Iran borders Iraq, Afghanistan, and Pakistan; it neighbors Saudi Arabia and sits astride the Strait of Hormuz.) Surely an Iran under attack would take counter-measures, to retaliate against the United States and those who cooperated with the U.S. strike. American planes need to take off and land, and any country that hosts those flights would be at war with Iran.

Even more problematic will be the consequences of the attack on the trajectory of politics within Iran. Such a massive strike will inevitably lead to considerable "collateral damage" -- that is, the death of innocent civilians. It would confirm the worldview painted by the current regime while delegitimizing moderate voices and interests. Whatever delay it had on the nuclear program, the attack would be the best thing that ever happened to Iranian hard-liners; support for the nuclear program and, more generally, anti-Americanism would soar.

Stopping bad, dangerous regimes from acquiring nuclear weapons is an urgent political goal. But a U.S. preventive strike against Iran is more likely, especially after a after a very short while, to guarantee, rather than prevent, that worst possible outcome. It invites a host of grave dangers to U.S. political goals in the region as well.

How, then, to stop the Iranian nuclear drive? The answer lies with diplomacy and sanctions, and especially with the future of Iranian domestic politics. Will sanctions 'work'? The question is misstated. The issue is, and is always, which measures are most likely to advance the political goals for which they are introduced? Preventive war would be counterproductive. Would sanctions force the current regime in Iran to change its stripes? No. The regime is relentless in its pursuit of nuclear weapons, and will continue to negotiate in bad faith hoping to stall action until they can present an atomic fait accompli.

The choice is not between 'negotiations' and 'taking them out': neither will succeed. But sanctions and diplomacy can shape the course of domestic politics within Iran, just as a military strike would, formatively and for the worse. Iran is a young country; the median age is twenty-seven. Most of the population was born after the Islamic revolution. Regime change will only come from within, and the best U.S. bet is to pursue those politics that will empower Iran's most attractive future leaders.

Jonathan Kirshner is Professor of Government and Director of the Reppy Institute for Peace and Conflict Studies at Cornell University.

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