In the final analysis, any US presidential decision on launching a defensive first strike against Iran will be based upon various tactical and strategic expectations. This means, inter alia, a determined focus on certain practical elements of operational success. Nonetheless, corollary questions of law must not be dismissed out of hand.
This obligation obtains even for a president who now calls openly for Iran's "obliteration," a belligerent cry that effectively undermines rather than reinforces US nuclear deterrence.
The pertinent facts are utterly plain and unassailable. To begin, it is increasingly unreasonable to expect that an American preemption against Iran could meaningfully succeed. Rather, for the United States, the probable costs of any such strike would plausibly exceed the expected benefits. In more expressly precise strategic parlance, a preemptive first strike by the United States would be irrational.
Even an American president so routinely dismissive of international law should at least remain aware of relevant legal considerations. Of course, before he could manage this transformation, Mr. Trump would first have to clarify what he is tangibly seeking in Iran. Is he looking only for the right to inflict certain variable harms upon that state if Iran should once again shoot down an American drone or be responsible for some similarly hostile action?
Or is Trump thinking primarily about preventing a nuclear Iran and staving off that serious problem at absolutely all costs?
Presently, it's very hard to tell. After all, the president's stream-of-consciousness comments concerning vigilance against Iran are less than specific and manifestly disjointed. Moreover, ignoring that the prospective credibility of a US nuclear deterrent threat could vary inversely with the magnitude of that threat, he is creating conditions that would plausibly obstruct America's principal primary intra-crisis obligation.
This is the foreseeable US obligation to achieve "escalation dominance" vis-à-vis Iran without stumbling into a catastrophic war. By threatening "obliteration" at the outset, Trump could effectively preclude any manageable sequence of bilateral escalations.
What next? To begin, Trump and his senior policy counselors will need to better understand and elucidate their desired military objectives in this particular theatre. Here, considerations of law will expectedly follow more primary considerations of strategic objective, but such legal considerations must not be excluded altogether. Already, the Trump administration has demeaned and marginalized the established collective security functions of the United Nations. This amounts to a willful disregard of the world's most conspicuously binding multilateral treaty, the UN Charter.
In its coherent totality, international law is designed to ensure the safety of all states in what amounts to a continuously anarchic world. Accordingly, its evident rules include the “inherent” right of individual or collective self-defense. At times, this basic or "peremptory" prerogative of states may be exercised not only after an armed attack has already been suffered (the legal expectation codified at Article 51 of the UN Charter), but also, on occasion, in advance. The UN Charter is a broadly authoritative agreement to which the United States is an original party and from which individual state members cannot pick and choose whatever is presumptively most convenient or cost-effective.
What are the permissible times for launching a preemptive attack – that is, a defensive strike that would qualify as "anticipatory self defense?" The answers involved in such multi-layered questions are potentially urgent for US President Trump, especially in the persistently dense case of Iranian nuclear weapons development. Is Tehran expanding its efforts in such a worrisome development? If so, are these expansions in verifiable violation of authoritative international law, or are they now more-or-less allowable – perhaps especially because of a prior and willful US withdrawal from the 2015 JCPOA agreement?
In dealing with such complex matters, we may reason from the general to the particular. What does world law say about preemption in general? Although the established rules of the UN Charter reserve the right of self-defense exclusively to states that have already suffered an armed attack, an equally valid customary legal norm may permit a first use of force if the danger posed is "instant, overwhelming, leaving no choice of means and no moment for deliberation."
Drawn from an 1837 incident in military history known as the Caroline (concerning the unsuccessful rebellion in Upper Canada against British rule), this usually inconspicuous doctrine builds upon the foundational seventeenth-century legal writings of celebrated jurist Hugo Grotius.
Self-defense, proclaims the Dutch scholar in The Law of War and Peace (1625), may be permitted "not only after an attack has already been suffered, but also in advance, where the deed may be anticipated." In his later text of 1758, The Right of Self-Protection and the Effects of Sovereignty and Independence of Nations, Swiss jurist Emmerich de Vattel similarly affirms: "A nation has the right to resist the injury another seeks to inflict upon it, and to use force and every other just means of resistance against the aggressor."
The jurisprudential writings of both Grotius and Vattel were well-known to the founding fathers of the United States, especially Thomas Jefferson. They are altogether unknown to the current American president.
Questions must be answered. Is there any discoverable evidence that Iran seeks to "inflict injury" upon the United States, either gratuitously or with some larger plan somewhere in mind? Even if such evidence were capably produced by the White House, any subsequent US defensive strikes would still need to meet standard "Law of War" criteria known as "discrimination," "proportionality" and "military necessity."
Even a US invocation of "anticipatory self defense" could not automatically allow President Trump any operational carte blanche in choosing any purposefully remediating uses of force.
There is more. International law has multiple and sometimes contradictory sources. Article 51 of the UN Charter, limiting self-defense to circumstances following an armed attack, does not override the equally valid customary right of anticipatory self-defense. As for customary international law, it is most prominently revealed at Article 38 of the (UN) Statute of the International Court of Justice.
Still, the actual conditions under which an expression of anticipatory self defense would conceivably be lawful must require enemy threats that are "instant," "overwhelming" and discernibly "imminent in point of time."
There is more. In rendering this country's indispensable strategic judgments, President Trump should expressly recall Article VI of the US Constitution and related US Supreme Court decisions. To wit, both sources proclaim unambiguously that international law is part of the law of the United States.
To be in compliance with his own oath of office, President Trump must first consider international law as an integral part of US law, and, correspondingly, as fully binding law. The confirming Supreme Court case here is the Paquete Habana (1900). In much broader connections, William Blackstone's seminal Commentaries were the principal foundation of all early United States law. In essence, his Commentaries on the Law of England represented the original legal system of the United States.
For Donald Trump, there remains one more singularly important clarification: The Caroline case decision notes an implicit distinction between preventive war (which is never legal) and preemptive war, which can be lawful or even law-enforcing. Anticipatory self-defense is never permitted to protect a state against some seemingly emergent threat; it is potentially permissible only when the "danger posed" is both "instant" and "overwhelming."
Using such a limiting jurisprudential framework, it is very doubtful that this US president could presently construct even a minimally valid legal argument for launching a preemption against Iran. This would be the case even if the considered American operation were based on authentically valid considerations of national self-defense and if it were limited meticulously to certain presumptively nuclear military targets. In law, a much more compelling case for preemption could be made by the State of Israel, which is vastly more vulnerable to any forthcoming Iranian nuclear developments than the United States.
Israel is literally half the size of an American lake (Lake Michigan) and could face sudden and complete annihilation from almost any future Iranian nuclear attack.
A related and sometimes derivative danger to Israel is posed by terrorist group surrogates. If not kept distant from receiving nuclear weapons or fissile materials from Iran, such proxies could possibly inflict grievous harms upon variegated Israeli targets. In principle, at least, such future harms could be nuclear, including determined rocket attacks against the Israeli nuclear reactor at Dimona.
This sort of attack was already attempted by Hamas several years back, but (thankfully) without success.
In the future, by striking a nuclear reactor core inside Israel, a non-nuclear insurgent adversary such as Hamas or Hezbollah could conceivably deliver authentically nuclear harms to the Jewish State.
Where does all of this leave US President Donald Trump? Operationally, any significant use of preemptive force against Iran would almost certainly initiate a wider cycle of attack and counter-attack, destabilizing the entire region and significantly expanding Israel's overall strategic vulnerabilities. The likelihood of these markedly unwelcome consequences would likely increase in rough proportion to US inflicted harms.
This suggests that if the American president's determined military objectives were designed to halt Iranian nuclearization, these American efforts could achieve some limited success but only at much greater overall strategic cost. As for any capable legal assessments, it is almost certain that any preemptive strike against Iranian targets ordered by Donald Trump – even if exclusively military or hard-target oriented – would represent a prima facie act of US aggression.
Mr. Trump should now be seeking assorted other remedies.
Louis René Beres, a frequent contributor to IsraelDefense, is Emeritus Professor of International Law at Purdue. He lectures and publishes widely on matters of Israeli security and nuclear strategy.