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PolicyWatch 3226

Deterring Iran’s Next Attack

Michael Eisenstadt

Also available in العربية فارسی

December 11, 2019

Since a maximum pressure policy requires maximum deterrence, the president should avoid tweets and actions that undercut U.S. credibility regarding the use of force, while authorizing the requisite rules of engagement.

Senior U.S. officials have warned in recent days that Iran may be preparing to launch new attacks in the Middle East as part of its campaign to undermine the Trump administration’s maximum pressure policy. Facilities used by U.S. troops in Iraq have already seen an uptick in rocket strikes, including nine in the past five weeks alone. No Americans were killed in these attacks, but the increase in fire and the reported movement of Iranian missiles into Iraq are potential harbingers of lethal attacks on U.S. personnel, or even a reprise of the audacious September 14 drone and cruise missile strike on Saudi oil facilities. Some officials are also concerned that Iran may target other critical infrastructure this time around, such as Gulf desalination plants.

As a result, Washington is reportedly considering the deployment of 4,000-7,000 additional troops to the region, beyond the 14,000 that have been sent there since May. The precise force mix under consideration is unknown, though it will likely include plus-ups of the assets needed to prevent a repeat of previous attacks, such as warships to protect oil tankers, air and missile defenses to protect critical infrastructure, and stealth fighters to protect high-value airborne platforms and preserve U.S. aerial freedom of action. Defending every high-value target is impossible, however, so deterrence remains the best way to prevent new attacks, halt further escalation, and protect U.S. interests in the Gulf. New deployments will therefore need to be backed up with other measures to bolster deterrence.


Washington’s maximum pressure policy requires maximum deterrence. The severe economic pressure generated by efforts to cut Iran’s oil exports to zero have already spurred Tehran to lash out militarily, and will likely do so again. Yet rather than helping to prevent such attacks, President Trump’s words and deeds have often undermined U.S. deterrence—from his repeated pledge to end U.S. involvement in the region’s “forever wars,” to his partially fulfilled declarations that all U.S. troops will be withdrawn from Syria. Such moves have probably led Tehran to conclude that the president lacks the stomach for a fight, and that at the very least it can target U.S. allies with impunity.

Thus, when Iran mined four tankers belonging to U.S. allies on May 12 and two more on June 13, the lack of a U.S. military response seemingly emboldened the regime, perhaps leading it to down a U.S. Global Hawk drone on June 20. President Trump authorized a limited cyberattack in response to that shootdown, further underscoring his desire to avoid military action. Likewise, his subsequent tweets seemed to reinforce the impression that Tehran could freely attack America’s allies. On June 24, he noted that “other countries...should be protecting their own ships” in the Gulf; a day later, he wrote that an attack on “anything American” would be met with “overwhelming force.” Iran’s major drone/missile strike on Saudi oil facilities came less than three months later.

Accordingly, Washington’s main deterrence challenge is one of credibility, not capability. To deter additional attacks, U.S. rules of engagement need to authorize the use of force to protect allies. The maritime ROE for countries participating in the International Maritime Security Construct reportedly allow this, but Washington needs to further demonstrate its commitment to potential military responses against attacks in all relevant domains—sea, air, land, and cyberspace. This includes making Tehran understand that it will get worse than it gives in any future exchanges.


Washington has generally opted for deterrence by denial in its interactions with Iran, trying to convince the regime that any attacks it attempts will be thwarted—that is, naval mines will be cleared, strikes on merchant vessels will be foiled, terrorist plots will be disrupted, and missiles and drones will be intercepted. But this approach permits Tehran to assess beforehand the risks and costs it is likely to incur to achieve its goals, potentially lowering the bar for it to strike.

Washington therefore needs to allow for deterring by punishment as well, such as threatening assets that Tehran truly values and being unpredictable in ways that make it difficult for regime leaders to calibrate risk. Otherwise, Iran will continue to test coalition defenses without paying a price. It is not clear, however, if America’s current ROE authorize such an approach—and, if they do, whether this fact has been conveyed to Iran.


It may sometimes be possible to deter Tehran by communicating awareness of an impending Iranian military operation, if doing so reduces its prospects for success. Yet when U.S. officials indicated awareness of an imminent Iranian attack in May, and new U.S. military deployments accompanied those announcements, they did not stop Tehran from undertaking the May-June tanker attacks.

Publicly disclosing evidence of the regime’s role in ostensibly “deniable” actions is also unlikely to deter future attacks. After all, Iran often leaves hints of its role. Mines used to disrupt U.S.-led convoy operations during the Iran-Iraq War often bore Iranian markings, as did weapons transferred to pro-Iran proxies in Iraq (after 2003) and Yemen (after 2015). Similarly, computer code written for malware used in Iranian cyberattacks has often incorporated telltale Farsi terms.

Thus, while Iran generally prefers the advantages of surprise and deniability, the absence of either will not necessarily deter it. Even so, exposing Tehran’s role is still useful because it can help shape international opinion and convince other countries to aid U.S. counter-efforts.


Tehran has accused Washington of fomenting the recent unrest in Iran, Lebanon, and Iraq. If mass protests resume and intensify inside Iran, the regime might lash out militarily against the United States out of a sense of desperation and vulnerability. Yet if Tehran perceives threats on multiple fronts, experience suggests it might eschew a response altogether in order to avoid overextending itself in a time of peril.

There is also a chance that the regime’s ongoing tensions with Israel might cause the heretofore separate U.S. and Israeli conflict tracks with Iran to converge, especially if a strike in Iraq attributed to Israel produces heavy casualties there. Such an outcome would be much less likely if the United States were to strengthen its deterrent posture.


Experience shows that once Tehran chooses a strategic direction, deflecting it from this course is often difficult; yet it will often back down when met with a firm response, renewing its challenge at another time and place. Thus, while deterrence is difficult due to asymmetries in motivation between the Iranian regime (which may believe it is fighting for its survival) and the United States (which is not), Washington should do whatever it can to force Tehran—at the very least—to curtail the tempo and scope of its operations, choose less lucrative targets, and use less effective means for its attacks. This approach may reduce the costs that Tehran can impose as well as the potential for escalation.

For this to occur, however, the Trump administration needs to eschew statements and steps that undercut deterrence, better align the ends, ways, and means of U.S. strategy, introduce greater uncertainty into Tehran’s cost-benefit calculus, demonstrate greater U.S. acceptance of risk, and present Tehran with threats from multiple directions, so that it perpetually has to prioritize its responses. When dealing with difficult actors like Iran, sometimes Washington must be prepared to escalate a situation in order to ultimately de-escalate it, toward the goal of resolving the crisis nonviolently.

Michael Eisenstadt is the Kahn Fellow and director of the Military and Security Studies Program at The Washington Institute.