I am no fan of the Trump Administration, which in its short life has attempted many illegal acts. But neither do I automatically conclude that everything it does is illegal, as a matter of international or domestic law. Nor can I stomach cynical assertions by the same Russian regime that has illegally annexed Crimea and supported terrorism in Eastern Ukraine that the Trump Administration’s April 6, 2017 strikes targeted against the Syrian airfield that had launched Assad’s renewed use of chemical weapons on innocent civilians last Tuesday, constitutes illegal “aggression” in violation of Article 2(4) of the United Nations Charter. Nor finally, absent further facts, do I conclude as a matter of U.S. law that the President has engaged in unconstitutional executive use of the war powers.

Let us separate the legal issue –were the strikes lawful?–from the complex policy question-what should the U.S. do about Syria?  As a matter of law, in a 2016 article (see pp. 1004-1015 here), I suggested the following test for judging the international lawfulness of claimed humanitarian interventions:

(1) If a humanitarian crisis creates consequences significantly disruptive of international order—including proliferation of chemical weapons, massive refugee outflows, and events destabilizing to regional peace and security—that would likely soon create an imminent threat to the acting nations (which would give rise to an urgent need to act in individual and collective self-defense under U.N. Charter Article 51);

(2) a Security Council resolution were not available because of persistent veto; and the group of nations that had persistently sought Security Council action had exhausted all other remedies reasonably available under the circumstances, they would not violate U.N. Charter Article 2(4) if they used

(3) limited force for genuinely humanitarian purposes that was necessary and proportionate to address the imminent threat, would demonstrably improve the humanitarian situation, and would terminate as soon as the threat is abated.

In particular, these nations’ claim that their actions were not wrongful would be strengthened if they could demonstrate:

(4) that the action was collective, e.g., involving the General Assembly’s Uniting for Peace Resolution or regional arrangements under U.N. Charter Chapter VIII;

(5) that collective action would prevent the use of a per se illegal means by the territorial state, e.g., deployment of banned chemical weapons; or

(6) would help to avoid a per se illegal end, e.g., genocide, war crimes, crimes against humanity, or an avertable humanitarian disaster, such as the widespread slaughter of innocent civilians, for example, another Halabja or Srebrenica. To be credible, the legal analysis of any particular situation would need to substantiate each of these factors with persuasive factual evidence of: (1) Disruptive Consequences likely to lead to Imminent Threat; (2) Exhaustion; (3) Limited, Necessary, Proportionate, and Humanitarian Use of Force; (4) Collective Action; (5) Illegal Means; and (6) Avoidance of Illegal Ends.

It is early to judge whether the Trump Administration’s April 6 actions satisfy this standard, particularly points (3) and (4).  But if they did, recognition of a customary international law “affirmative defense” against a claim of Article 2(4) violation would not, as Marty Lederman suggests, “require an amendment to the Charter to effect.” Instead, as I argued in 2016, the nations supporting the U.S. action would likely claim

an ex post exemption from legal wrongfulness. The International Law Commission’s Articles on State Responsibility recognize, for example, that extreme circumstances such as distress and necessity would preclude claims of international wrongfulness against an acting state and permit certain forms of countermeasures to stop illegal acts by others. Whether the collective action would ultimately be judged internationally lawful would then depend critically on what happened next, particularly if the Security Council condoned the action after the fact. … We have reached a lawmaking moment, where international lawyers in and out of government need to discuss and define a narrow “affirmative defense” to Article 2(4) of the U.N. Charter that would clarify the contours of an emerging lawful exception to a rigid rule [that humanitarian intervention is “per se illegal”]. Reading an implied narrow exception into that rigid rule would better balance the risks of over- and under-action in the most dire situations.

Nor do I believe the President has acted unlawfully under domestic law, for the reasons stated in pp. 1015-16 here, particularly if the April 6 strikes turn out to be a one-time response to Assad’s chemical attacks. The right move now would be for the President to ask Congress to endorse publicly his April 6 actions, but in this sad political climate, that obviously might well not happen.

The harder questions going forward, though, are of policy, not law. What happens next?

What is long overdue, as former Deputy Secretary of State Tony Blinken correctly argues in today’s New York Times, is for the Administration to use whatever opening may be created by the strike to pivot to a longer-term “smart power” approach to Syrian diplomacy: not just sending Assad a message never again to use chemical or biological weapons, but integrating the U.S. military campaign against ISIL with a broader strategy against Assad: what the late Richard Holbrooke would have conceived of as a “Syrian Dayton,” jumpstarting multilateral diplomacy to achieve an effective cease-fire in Syria’s brutal civil war and pursuing accountability, while moving toward a negotiated transition of power.

And make no mistake: President Trump cannot on the one hand sensibly launch missiles against Assad for his brutality toward Syria’s innocent children, while simultaneously imposing his own overbroad blanket ban upon the entry of those same children and their parents into the United States under his revised March 6 travel ban, which more than 40 former top national security officials have explained cannot be justified on either national security or foreign policy grounds.

In sum, a one-time Tomahawk strike does not a Syria policy make.  But it can mark a turning point. In negotiating this important moment of lawmaking that is now upon us, the Administration must start to tackle the broader policy challenges that face it in Syria: ending a brutal civil war; helping to forge a stable political solution; mitigating a refugee crisis; ensuring accountability; and sensibly coordinating our actions against Assad with the ongoing military campaign against the Islamic State.  Going forward, all of this will require not just bombs, but diplomacy; not just tweets, but thoughtful diplomatic proposals; not just “America First,” but genuine American multilateral leadership.