Mutual Defense Treaties and Presidential War Powers

Unilateral presidential defense of non-treaty allies like Israel, Taiwan, and the Arab Gulf States dominates current U.S. foreign policy. But courts have not established the constitutionality of unilateral defense of non-treaty allies. This Article posits that the existence of a mutual defense treaty makes a decisive difference for the constitutionality of unilateral intervention to defend an ally. A treaty can serve as an authorization to use military force (AUMF). Without such a treaty, intervention to protect an ally can only be considered constitutional under the most expansive pro-executive interpretations of presidential war powers.

     The Supreme Court has never squarely addressed the relevance of treaties for presidential war powers. But the treaty-as-AUMF hypothesis fits constitutional text, relevant case law, and a history of congressional acquiescence dating back to President Madison’s occupation of Spanish West Florida in 1810. Similarly compelling evidence suggests Congress has not acquiesced in unilateral presidential action to defend non-treaty allies.

     Judicial enforcement of a treaty-based AUMF interpretation could not come at a more opportune time. Unilateral executive deployments have incentivized the leaders of non-treaty allies to cultivate partisan and financial relationships with presidents, inviting corruption and incentivizing election interference. Treaty relationships, based on a necessarily bipartisan two-thirds ratification vote in the Senate, have the potential to lead to healthier and more productive alliances. If a mutual defense treaty does not constitute an AUMF, then ratified defense treaties have little value except as a show of moral support—the legal equivalent of a pledge of “thoughts and prayers” for allies.