In May of 2018, the Trump administration pulled out of the 2015 multi-nation Iran nuclear deal and began a campaign of “maximum pressure,” imposing new sanctions on Iran with the aim of renegotiating deal. One year later, the situation is tense after several attacks on international oil tankers in or near the Strait of Hormuz and, on June 20, the downing of a U.S. Military drone by Iran. The U.S. seemed to be moving toward a possible war when last week President Trump considered a military response. Here, international law expert Allen Weiner discusses the Iran conflict, law, and the possibility of a diplomatic solution.

President Trump said that plans were in place for an airstrike on Iran last Thursday night (June 20), but it was called off because he thought it would not be a “proportionate” response to the downed American drone. Under what circumstances can the president attack another country?

It’s always important to remember that any proposed use of force has to be judged under two different bodies of law—both international law and domestic law. As an international law matter, the United States would be justified in using necessary and proportionate force in self-defense in response to an attack against a U.S. drone. But this would be true only if the U.S. drone was operating, as it is allowed to do, in international airspace. As we know, this is disputed. If one of our military drones strayed into Iranian airspace, Iran’s decision to shoot it down would not provide the U.S. with a self-defense justification.

Is the President required to seek Congressional approval for a military action? Were those conditions met?

As a matter of domestic law, Congress has the power to “declare war,” but it has long been recognized that the President, under his Commander-in-Chief power, may authorize the use of force in situations of more limited hostilities that do not rise to the level of “war.” Exactly where the line is, of course, remains a hotly contested issue. But a limited use of force against Iran for downing a U.S. drone would be consistent with the exercises of force that Presidents have authorized many times in the past.

Iran downed a U.S. Military drone last week, because they believed it to be in their country’s airspace. The Trump administration disputes this. Earlier, two oil tankers were attacked—the administration reportedly believes by Iran. What do you make of this? Is it as some commentators have speculated that the Iranian Revolutionary Guard sometimes acts independently of, and more aggressively than, the government?

To begin with, Iran—like the United States—has domestic politics, and those politics are complicated. I don’t think we understand them terribly well in the United States, so my comments—along with those of other U.S.-based experts—need to be taken with a big grain of salt. That said, I have doubts that the Islamic Revolutionary Guard Corps (IRGC) would risk a military confrontation with the United States without Iranian policy being coordinated at the top levels of government.

How do you account for Iran’s actions? Have they been pushed to act?

Iran is under great pressure as a result of U.S. sanctions imposed after the U.S. withdrew from the Joint Comprehensive Plan of Action (JCPOA), or the so-called nuclear deal. Those sanctions are biting more deeply than the Iranians had predicted. I believe Iran has taken a deliberate— although highly risky—decision to demonstrate to the United States that there are potentially significant costs for the U.S. and its allies if the U.S. pursues a strategy that includes only sticks, with no possibility of carrots.

But will the administration’s tough sanctions bring Iran back to the negotiating table?

Part of what makes this so dangerous is that the Iranians—at least publicly—have so far indicated that they have no interest in renewing negotiations with the U.S., which makes it hard to see how the parties are able to climb down from escalating tensions.

Can you talk about U.S. sanctions and how America’s allies have responded to them?

Most of our allies—as well as China and Russia—oppose our sanctions, which were re-imposed last year. For major importers of Iranian oil like India or South Korea, this affects the cost and security of their energy supplies. Our European allies, who were America’s partners in negotiating the JCPOA, still support the basic logic of that arrangement, under which Iran’s nuclear program would be constrained so as to reduce, or at least delay, the risk of Iran acquiring nuclear weapons. Iran, in exchange, expected significant sanctions relief and the opportunity for enhanced integration in the international economic system. Until recently, Iran had been complying with its commitments regarding its nuclear program, but U.S. sanctions, as we have seen, are putting great pressure on the basic exchange on which the JCPOA was based. Iran is no longer fulfilling some of its nuclear commitments, in particular with respect to uranium enrichment, and it has signaled that it will soon stop fulfilling others. To the extent U.S. sanctions cause the JCPOA to unravel and collapse, our allies oppose them.

Also, many countries in principle object to the extraterritorial aspects of U.S. sanctions; it galls them that the U.S. has adopted policies that—contrary to their own foreign policy preferences—seek to inhibit their companies from doing business with Iran.

There was an interesting report last week about a visit to Tehran by the German foreign minister and the announcement that a new European payment system, designed as an alternative to the dollar-based one, would soon be ready. This visit was made in coordination with Britain and France, both of which helped create the new payment mechanism, called INSTEX. What do you think motivated our closest allies to do this?

As noted, our European allies continue to support the JCPOA, and they do not object to their companies doing business with Iran. U.S. sanctions work in part by requiring foreign banks involved in transactions with Iran to deposit any funds due to Iran under those deals in an account in that bank’s country, i.e., not in Iran. This means Iran can’t actual repatriate hard currency it earns from oil sales in international trade. In a sense, the issue is not technically a “dollar” issue, it’s a currency issue. But since most international trade, especially oil trade, is done in dollars, that’s a distinction without a difference. In an effort to preserve the JCPOA, the Europeans accordingly are seeking to devise a way for their companies and banks to work around U.S. sanctions.

I would not read too much into the timing of the announcements about INSTEX. The Europeans have been working on trying to establish such a mechanism, which they also refer to as a Special Purpose Vehicle, since the U.S. withdrew from the JCPOA and reinstated sanctions last year. The goal of the mechanism is to surmount U.S. sanctions by essentially providing for barter payment; instead of receiving currency for oil exports, Iran would receive commodities. At this point, INSTEX will be focusing on providing Iran with food, medicine, and medical device.

Do you see a diplomatic way forward to calm tensions in the region?

Both countries have leaders who use highly aggressive and nationalistic language but who at the same time want to avoid a serious escalation. Neither President Trump nor Supreme Leader Khamenei wants a war to erupt. But both leaders have a strong interest in signaling resolve—including a willingness to use force—to the other side. They are also under pressure to manage their domestic hardliners. This combination of factors creates tremendous escalatory pressure.

Because each side is so entrenched in the positions it has staked out – the U.S. has announced a long list of demands that Iran would have to meet to be treated as a “normal country,” and Iran has declared its refusal to negotiate with the United States—it is difficult to see much hope that the countries will initiate any meaningful bilateral discussions. The best that we can hope for, I think, is that intermediaries might be able to carry messages between the parties through which each side reaffirms its desire to avoid further escalation. The recent visit of Japanese Prime Minister Shinzo Abe is notable in this regard.

The fundamental tension is that Iran seems to have decided that it can no longer wait for either the Europeans or House Democrats to alleviate the pressure of U.S. sanctions. It looks like the Iranians have decided that they instead must demonstrate their ability to impose costs on the U.S. and its allies as a way of countering U.S. pressure. If so, Iran is likely to continue engaging in destabilizing activities, like attacks on neutral shipping, that could at any moment trigger a U.S. military response. I accordingly expect the coming months to be a very tense time in the region. I fear that the risks for Iran and the United States to be drawn into an armed conflict that neither of them really wants are high.

Allen S. Weiner, JD ’89, is an international legal scholar with expertise in such wide-ranging fields as international and national security law, the law of war, international conflict resolution, and international criminal law (including transitional justice). His scholarship focuses on international law and the response to the contemporary security threats of international terrorism, the proliferation of weapons of mass destruction, and situations of widespread humanitarian atrocities. He is a Senior Lecturer in Law and Director of the Stanford Program in International and Comparative Law at Stanford Law School.