Co-authored by Elise Meyer

On the evening of April 6, the Trump Administration launched a cruise missile strike against the Assad regime in response to the use of chemical weapons against civilians earlier in the week. The Trump Administration has not set forth a legal justification for the airstrike. Given the Assad regime’s human rights record, among the strongest legal justifications to support the Trump administration’s action is the doctrine of Responsibility to Protect.

In the early days of the Syrian conflict when former President Obama was presented with a similar situation, I co-authored a law review article arguing that Responsibility to Protect provided the strongest legal justification under international law for military intervention. Five years later in the context of the Trump Administration’s airstrike, this argument still rings true.

While international legal experts are discussing sovereign consent, UN Security Council authorization, and self-defense, Responsibility to Protect remains the most viable legal basis for the airstrike. Responsibility to Protect addresses concerns about the lack of a UN Security Council resolution and consent while providing a stronger justification than the self-defense doctrine, which experts agree would be difficult if not impossible to establish.

Responsibility to Protect first entered the scene as an international legal concept in 2001 when the International Commission on Intervention and State Sovereignty articulated that in order to maintain sovereignty, states must protect their people from atrocity crimes. In 2005 and 2009 respectively, the UN General Assembly and Secretary-General Ban Ki-moon both endorsed the Responsibility to Protect concept. According to the UN, the Security Council has referenced Responsibility to Protect over fifty times in resolutions and presidential statements since 2005. Moreover, the Security Council embraced the doctrine of Responsibility to Protect in its resolution to justify the use of force in Libya, and its precursor doctrine is generally understood as the basis for the NATO intervention in Kosovo.

There are three elements of Responsibility to Protect according to the UN Secretary-General’s 2009 report. First, states have an obligation to protect their populations from atrocity crimes. Second, when there is convincing evidence of ongoing atrocity crimes, and a state is unable or unwilling to stop them, the international community must exhaust peaceful options, such as diplomacy and targeted sanctions. Third, after the exhaustion of peaceful options, the international community may use military force to protect civilians as a last resort.

Ideally, the Security Council would authorize humanitarian intervention. However, its failure to do so does not obliterate the principle of Responsibility to Protect.

Given the nature of the Syrian crisis, the airstrikes satisfy these requirements. First, the UN has already made the legal determination, based on local and international monitoring, that the Assad regime is committing atrocity crimes. These include other chemical attacks, mass hangings in Saydnaya Prison, and war crimes associated with the battle for Aleppo. These crimes have resulted in close to 11 million displaced people and over 400,000 deaths.

Second, the parties have long since exhausted peaceful alternatives. Since 2012, there have been four major international attempts to negotiate a political solution to the conflict. These have increasingly revealed Assad’s unwillingness to genuinely commit to a peaceful settlement. Russian-led ceasefire talks in Astana have similarly failed to end Assad’s continued violation of international human rights law. Even targeted international sanctions have failed to incentivize Assad’s cooperation.

Given these circumstances, the international community can use military force for the limited purpose of stopping the Assad regime from continuing to commit atrocity crimes against Syrian civilians. Such military force must be proportionate and narrowly tailored to achieving the humanitarian goal. So far as we can tell, the airstrike fits within these parameters. The Trump administration declared the airstrike was intended to prevent and deter future chemical attacks. Indeed, the strike targeted the airbase from which the chemical attack originated.

While the Trump administration appears reluctant to provide a legal justification for the airstrike, it should in fact embrace the opportunity to justify its legitimate action based on the Responsibility to Protect doctrine. The administration should also use the opportunity to further refine and crystalize the doctrine, as it may have to rely upon this doctrine for future proportional strikes if it is in fact “prepared to do more” to stop the carnage in Syria and lay the foundation for a durable peace.

Dr. Paul Williams holds the Rebecca I. Grazier Professorship in Law and International Relations at American University and is the co-founder of the Public International Law & Policy Group (PILPG). He is a leading world expert in peace negotiations, post-conflict constitution drafting, and war crimes prosecution. In the course of his career he has assisted in over two dozen peace negotiations and post-conflict constitutions.

Elise Meyer is a Law Fellow with the Public International Law & Policy Group where she focuses on countering violent extremism and national security issues in East Africa. She is a graduate of the University of Chicago Law School.