Ukraine and War Powers: A Legal Explainer

The United States’ evolving response to Russia’s war against Ukraine – including the deployment of additional U.S. troops to eastern Europe and potentially additional arms transfers – has raised questions about the legal framework for the United States’ involvement in NATO, the obligations it creates, and the implications for presidential war powers. This article seeks to address some of these legal questions which bear on the allocation of war-making authority within the U.S. government.

Question 1: Does the deployment of additional U.S. forces to NATO members in eastern Europe constitute the introduction of U.S. forces “into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances” – and thus trigger the provisions of the 1973 War Powers Resolution (WPR) that require the President to withdraw troops within 60 days of such an introduction absent congressional authorization?

Answer: The reported troop movements have not thus far pulled the hostilities or imminent hostilities triggers of the WPR. The WPR seeks to prevent the President from taking the country to war on his own, and also encourages transparency with respect to troop movements that could be preparations for the use of military force. To this end, Section 4(a) of the WPR establishes reporting requirements, under which the president must report certain activities of U.S. armed forces within 48 hours to Congress if they have not already been authorized:

• First, the president must report when U.S. military forces are introduced into “hostilities” or “situations where imminent involvement in hostilities is clearly indicated by the circumstances.” Although not defined in the WPR, the executive branch has narrowly interpreted hostilities to mean “a situation in which units of the U.S. armed forces are actively engaged in exchanges of fire with opposing units of hostile forces” and imminent hostilities to mean “a situation in which there is a serious risk from hostile fire to the safety of United States forces.” (4(a)(1))

• Second, even if U.S. forces are not introduced into hostilities (or situations where they face the imminent risk of hostilities), the president must report the introduction of “combat equipped” forces into a country — which the executive branch reads as forces equipped with crew-served weapons such as machine guns requiring more than one person to operate and mortars. (4(a)(2))

• Third, the president must also report a substantial enlargement of such combat equipped forces in a country where such forces are already present. (4(a)(3))

Notably, under Section 5(b) of the WPR, the submission of a report under the first of these scenarios – introduction of U.S. forces into hostilities or situations of imminent risk thereof – also starts a 60-day clock for the withdrawal of U.S. armed forces from such hostilities (extendable to 90 days under certain circumstances) unless Congress declares war or otherwise enacts specific statutory authorization for the use of force.

Based on publicly available information, President Biden’s actions to date do not trigger Section…