The views expressed here are solely those of the author. They do not necessarily represent the views of the Naval War College, the U.S. Navy, or the Department of Defense.

Iran is committed to a nuclear-energy program, and it may be committed to nuclear weapons. Israel appears committed to preventing it from getting them. Prime Minister Benjamin Netanyahu has called Iran’s leadership a “messianic apocalyptic cult,” and the current composition of the Israeli cabinet is overwhelmingly hawkish on Iran. U.S. leaders have also declared that an Iranian nuclear program is unacceptable, though their rhetoric has been more restrained.

Suppose Israel or the United States launches a preventive military strike against the Iranian nuclear complex. They certainly have the capabilities to destroy large chunks of it. Even a unilateral Israeli strike would do significant damage to key sites, including the major enrichment center at Natanz. On the other hand, Israeli and American leaders might not be satisfied with the result. Given the revelation of previously hidden facilities, they might worry that Iran would still be able to pursue clandestine nuclear work even after absorbing a preventive attack. In any case, officials are likely to remain concerned as long as the Iranian regime remains in power. So while they can disable Iranian facilities and delay its progress towards the bomb, they will not be confident that they can permanently end the program. Israel and the United States cannot escape the problem of deterrence against a nuclear Iran.

In a previous post, I described four actions that the United States will seek to deter if Iran joins the nuclear club. First, it will seek to deter Iran from rapidly expanding its nuclear program in ways that could undermine the security of its fissile material. Second, it will seek to deter Iran from transferring nuclear technology to groups like Hezbollah. Third, it will seek to deter Iran from using nuclear weapons as cover for conventional aggression and stepped-up support to regional proxies. Finally, it will seek to deter Iran from using nuclear weapons in war.

The prospects for deterring each of these actions will suffer in the aftermath of a preventive attack.

Deterring a rapid expansion of the Iranian nuclear program will be much more difficult. Having been targeted already, Iran will have obvious incentives to disperse and conceal its remaining facilities, much as Iraq did after Israel’s strike against its Osirak reactor in 1981. Iranian leaders will also be tempted to increase the stockpile of weapons in order to ensure that at least some survive future strikes. Most important, an attack will empower hard-liners who have built the regime’s ideology on a foundation of resistance against the West. Attacking Iran will give them something new to resist.

Deterring the transfer of nuclear material to third parties will also be harder. Iran has historically exercised caution when dealing with groups like Hezbollah, withholding chemical weapons and other capabilities likely to provoke a direct confrontation with the United States. Iran would have less reason for caution in the aftermath of a preventive attack. On the contrary, it might conclude that dispersing some nuclear assets to regional proxies is the best way to protect them from repeated strikes.

Preventive action will complicate efforts to deter the use of nuclear weapons as cover for conventional aggression. Military strikes, especially if Israel is involved, will make it diplomatically tougher to sustain a regional counterbalancing alliance against Iran. During the Cold War, the United States was able to deter Moscow from acting against Western Europe in part through a strategy of denial; a strong NATO backed by U.S. hardware gave Soviet leaders reason to doubt that a conventional offensive would succeed. The United States is taking steps to shore up the conventional balance against Iran for the same reasons today, selling arms to its neighbors and declaring a defense umbrella over the Gulf. Maintaining solidarity will be difficult after a preventive strike, however, because regional states will face significant domestic pressure to distance themselves from Washington. Although Iran’s nuclear program evokes mixed feelings in the region, a majority of Arabs oppose international attempts to force it to give up its nuclear program. A preventive attack against that program is likely to lead to public outrage and create new political risks for leaders who would otherwise cooperate with the United States.

The ultimate danger is that Iran would use nuclear weapons in war. Deterring nuclear use will require an explicit or implicit threat of devastating retaliation, regardless of whether the United States or Israel strikes first. But the threat is not enough. Effective deterrence will also require complementary assurances that Iran will be spared such devastation as long as it complies. Iran will have less reason to be cautious if it does not receive this kind of assurance, especially if it believes that escalation will force its enemies to sue for peace on more favorable terms. U.S. assurances may not be credible in the wake of a preventive attack, however, if Iran concludes that U.S. leaders are implacably hostile and untrustworthy. In this case, it may be impossible to convince them that the United States will show restraint as long as Iran does not escalate to the nuclear level. In short, a preventive military strike is likely to produce enduring hostility and mistrust, both of which will hinder war termination and make it harder to control escalation. Iranian leaders might take extraordinary risks—including nuclear risks—rather than face the prospect of catastrophic defeat.