I am more of an Iran hawk than Bridge Colby or Austin Long, but they raise an important question in their case against attacking Iran:

[P]erhaps the most important argument against attacking Iran has received less attention. That is that none of the attack proponents can give a sensible answer to the question General David Petraeus posed at the beginning of the Iraq war: “How does this end?” Kroenig and other advocates for war note, correctly, that a strike against Iran could do substantial damage to Iran’s program. But they fail to explain how the United States will prevent Iran from simply restarting its program, this time in deadly earnest. Moreover, they don’t explain why such strikes won’t contribute to the immediate rallying of the Iranian people around the otherwise reviled regime.

This is a fairly familiar argument. What is much less familiar is Colby and Long’s argument regarding the extensive military campaign required to police Iran post-attack:

[T]he United States should be prepared to conduct repeated strikes over a long period of time to ensure the Iranian nuclear program is kept down. Unsurprisingly, Kroenig and others shy away from this answer, as it is a recipe for perpetual war. The cost in lives, resources and America’s international reputation would be formidable, especially if done without diplomatic cover and international support that probably wouldn’t be forthcoming. Yet, even under the most favorable conditions in which Iranian retaliation stayed limited and international support was forthcoming, a long-term, limited-strike campaign might not work at a level of effort and damage in line with U.S. aims. Regular U.S. strikes on North Vietnam over a period of seven years under highly favorable international conditions failed woefully either to convince Hanoi to change its fundamental strategy or substantially degrade the communist war effort. The North Vietnamese resolutely repaired bridges, depots and roads. More recently, limited allied air strikes against Iraq in the 1990s didn’t force Saddam Hussein’s compliance with UN Security Council Resolutions. Moreover, as happened in Vietnam, such strikes likely would become more difficult over time. The Russians, for example, have refrained, thanks to Western diplomacy, from selling Iran advanced long-range surface-to-air missiles that could make strikes more difficult. They probably wouldn’t be so forbearing if strikes were conducted without their prior and explicit approval, which Moscow isn’t likely to give.
But the primary challenges to U.S. striking power would be political and stem from the difficulties in sustaining a coalition supportive of such measures over time. Recall that the consensus behind Clinton-era strikes on Iraq fell apart as the policy continued with no end in sight. Ultimately, such a campaign would be unlikely to succeed absent a fundamental change in the perception of the Iranian government. Failing such a change, a perpetual-strike campaign would leave us in a worse situation. Tehran would have an added incentive to obtain a nuclear capability to strengthen its deterrent against attack. U.S. military power would be shown to be of limited value. And an international coalition against Iran’s nuclear program would fall apart. Finally, if the Iranian regime did succeed in acquiring a nuclear capability even after a sustained U.S. attack, it would be sure to be even more paranoid and on edge, with deeply worrying implications for how it would posture its nuclear arsenal. Since Tehran would reasonably believe the United States and other powers were aiming to take military action to deprive it of its nuclear weapons, Iran would have a strong incentive to take destabilizing steps to ensure those weapons were protected and, ultimately, that they could be used. [Emphasis added]

Rick Santorum has said that we must prevent the Iranians from gaining a nuclear weapon because, to paraphrase, the Iranian regime is not irrational and it does not fear death. If this is indeed true, and it is not clear that it is true (one gets the impression that much though not all of the Iranian elite is in fact very venal and primarily interested in amassing wealth and power for itself), a strike on Iran’s nuclear facilities would presumably deepen its paranoid millenarianism, thus fueling renewed efforts to acquire weapons and perhaps to launch terror attacks against the U.S. and its allies.

I’d say attacking Iran is a tougher call than some advocates acknowledge. My main concern is the cost-benefit calculation. Unfortunately, there are no inexpensive options, as deterrence will also prove expensive and disengagement from the region is, in my view, a pipe dream, in light of the central importance of the Gulf region to the global energy supply.