But if the Iran deal was a mistake, could the mistake be undone by withdrawing from the deal? The costs to the U.S. were sunk. The U.S. had given up the international sanctions regime in exchange for restrictions on Iran’s nuclear program that would expire in just a few years, so the dilemma of what do about it had only been postponed. Withdrawing from the deal would merely bring forward the day the U.S. would have to face the dilemma again, this time without the benefit of a united diplomatic front. In the meantime, Iran’s compliance with the deal’s limited verification regime (no military sites, no anytime-anywhere inspections, IAEA purview restricted to declared facilities) provided at least a minimal benefit.

Withdrawing from the Iran nuclear deal, then, did not ipso facto mean that the U.S. was returning to a strategy of containment backed by deterrence. If anything, withdrawing from the deal implied a policy of confrontation, but was the administration really committed to winning it? Trump’s foreign policy approach, which the Washington Post columnist Max Boot calls “belligerent isolationism,” does not shy from projecting American power abroad, but resists foreign commitments, and sometimes seems ambivalent toward the very allies needed for almost any strategy of confrontation to succeed.

David Frum: We’re just discovering the price of killing Soleimani

The administration’s approach to sanctions is a case in point. Sanctions have significantly diminished Iran’s oil revenue, with devastating effects. To soften the impact on world oil prices, America’s Gulf allies—principally Saudi Arabia and the United Arab Emirates—moved to replace the lost Iranian supply. Iran rightly saw all of this as a campaign of economic warfare, and responded by first attacking Saudi and Emirate oil shipments, then a major production facility in Saudi Arabi, and finally a U.S. drone. Yet the U.S. hardly responded to these provocations, no doubt leading many in Saudi Arabia and the UAE to wonder whether it mightn’t be safer to assume a more neutral posture toward Iran.

The U.S. only reacted with force when Iran openly orchestrated a series of attacks on the U.S. embassy in Baghdad and other installations in Iraq that left an American dead. The killing of an American without plausible deniability is a redline the government of Iran is not likely to cross again anytime soon. But will the credible enforcement of that redline be enough to shore up the multinational sanctions regime, or establish the level of containment necessary for stability in the region?

Any chance of containing Iran depends on strengthening America’s system of regional alliances—and especially on reviving the U.S. alliance with Iraq. Americans may not understand that, but Iran does. That’s why in recent weeks it escalated from attacks on U.S. Gulf allies to direct attacks on U.S. installations in Iraq. That’s why its principal response to the killing of Iranian General Qaseem Soleimani was to attack installations with U.S. personnel in Iraq. If Iran can expel the Americans from Iraq and cow America’s other Gulf allies into assuming a more neutral posture, it can dominate much of the Middle East, no matter what the level of US. forces in the region. In that case, the loss of Soleimani will have been more than worth it.

Iran may now be more hesitant to kill Americans. But if it isn’t afraid to challenge U.S. interests in other ways, then the Middle East is likely to get more dangerous in the months ahead, as Iran finds new ways of forcing America to choose between appeasement and a war that no American wants. That’s why returning to a strategy of containment, backed by clear and credible deterrence, is more urgent than ever.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.