¹ U.S. Dep't of State, Fact Sheet: U.S. Relations with Yemen (Feb. 2, 2017), at https:// www.state.gov/r/pa/ei/bgn/35836.htm.

² White House Press Release, Statement by NSC Spokesperson Bernadette Meehan on the Situation in Yemen (Mar. 25, 2015), at https://obamawhitehouse.archives.gov/the-press-office/2015/03/25/statement-nsc-spokesperson-bernadette-meehan-situation-yemen.

³ Id.

⁴ Id. (stating that “U.S. forces are not taking direct military action in Yemen in support of this effort”).

⁵ E.g., Matthew Rosenberg & Mark Mazzetti, U.S. Ship off Yemen Fires Missiles at Houthi Rebel Sites, N.Y. Times (Oct. 12, 2016), at https://www.nytimes.com/2016/10/13/world/middleeast/yemen-rebels-missile-warship.html (reporting that, as of October 2016, the U.S. military had “refueled more than 5,700 aircraft involved in the [Saudi-led] campaign”).

⁶ E.g., Missy Ryan, Civilian Casualties in Yemen Bring Charges of U.S. Responsibility for Saudi Actions, Wash. Post (Oct. 3, 2016), at https://www.washingtonpost.com/world/national-security/civilian-casualties-in-yemen-bring-charges-of-us-responsibility-for-saudi-actions/2016/10/03/29a9b606-864d-11e6-ac72-a29979381495_story.html (reporting that the Pentagon provided the Saudi military lists of “no-strike” locations, including civilian targets and infrastructure).

⁷ E.g., Wall, Robert, U.S. Military Working to Prevent Weapons Shortfall in Islamic State, Yemen Strikes, Wall St. J. (Nov. 10, 2015)Google Scholar, at https://www.wsj.com/articles/u-s-military-working-to-prevent-weapons-shortfall-in-islamic-state-yemen-strikes-1447143660 (reporting a November 2015 statement by a commander of the U.S. Air Force Central Command that the U.S. military had a small detachment of personnel helping coordinate activities in the Saudi Arabian center planning air strikes).

⁸ White House Press Release, Letter from the President – War Powers Resolution (Oct. 14, 2016), at https://obamawhitehouse.archives.gov/the-press-office/2016/10/14/letter-president-war-powers-resolution [hereinafter WPR Letter].

⁹ Id.

¹⁰ See Burdette, Zachary, Today's Headlines and Commentary, Lawfare (Oct. 13, 2016)Google Scholar, at https://www.lawfareblog.com/todays-headlines-and-commentary-1166.

¹¹ U.S. Dep't of Defense Press Release, Statement by Pentagon Press Secretary Peter Cook on U.S. Military Strikes Against Radar Sites in Yemen (Oct. 12, 2016), at https://www.defense.gov/News/News-Releases/News-Release-View/Article/972169/statement-by-pentagon-press-secretary-peter-cook-on-us-military-strikes-against.

¹² War Powers Resolution, Pub. L. No. 93-148, 87 Stat. 555 (1973).

¹³ WPR Letter, supra note 8.

¹⁴ Id.

¹⁵ This was not the first time former President Obama relied on his Article II powers to justify the use of military force abroad. See, e.g., Daugirdas, Kristina & Mortenson, Julian Davis, Contemporary Practice of the United States, 110 AJIL 587, 590 (2016)Google Scholar (discussing the administration's invocation of “unit self-defense”—grounded in the president's Article II authority as Commander in Chief—to justify air strikes in Somalia); Daugirdas, Kristina & Mortenson, Julian Davis, Contemporary Practice of the United States, 109 AJIL 174, 206–07 (2015)Google Scholar (quoting a WPR letter by Obama, justifying air strikes against the Islamic State based on the president's “constitutional authority to conduct U.S. foreign relations and [authority] as Commander in Chief and Chief Executive”); Crook, John R., Contemporary Practice of the United States, 105 AJIL 568, 574 (2011)Google Scholar (discussing President Obama's reliance on Article II powers to justify U.S. military actions in Libya).

¹⁶ WPR Letter, supra note 8.

¹⁷ See U.S. Dep't of Defense News, USS Mason Responds to Missile Threat off Yemen's Coast (Oct. 12, 2016), at https://www.defense.gov/News/Article/Article/971904/uss-mason-responds-to-missile-threat-off-yemens-coast; Lamothe, Dan, Navy Launches Tomahawk Missiles at Rebel Sites in Yemen After Attacks on U.S. Ships, Wash. Post (Oct. 12, 2016)Google Scholar, at https://www.washingtonpost.com/news/checkpoint/wp/2016/10/12/more-missiles-fired-from-rebel-held-territory-in-yemen-at-u-s-navy-ships.

¹⁸ U.S. Dep't of Defense News, supra note 17.

¹⁹ Id.

²⁰ Yemen Denies Targeting U.S. Warship, Saba News Agency (Yemen) (Oct. 13, 2016), at https:// www.sabanews.net/en/news443542.htm (quoting a Houthi military official for the allegation that “[t]hese allegations are unfounded and the army as well [as] popular forces have nothing to do with this action”).

²¹ U.S. Dep't of State Special Briefing, Senior Administration Officials on Yemen (Oct. 14, 2016), at https://2009-2017.state.gov/r/pa/prs/ps/2016/10/263158.htm.

²² Id.; see also Lamothe, supra note 17. For the Houthis’ asserted responsibility for the October 1 attack, see Army Destroys UAE Warship off Mocha Coast, Saba News Agency (Yemen) (Oct. 1, 2016), at https://www.sabanews.net/en/news442035.htm.

²³ U.S. Dep't of State Special Briefing, supra note 21.

²⁴ U.S. Dep't of Defense News Transcript, Department of Defense Press Briefing by Pentagon Press Secretary Peter Cook in the Pentagon Briefing Room (Oct. 13, 2016), at https://www.defense.gov/News/Transcripts/Transcript-View/Article/973367/department-of-defense-press-briefing-by-pentagon-press-secretary-peter-cook-in.

²⁵ Id.

²⁶ U.S. Dep't of State Special Briefing, supra note 21.

²⁷ Id. Although this point has not been discussed in relation to these strikes, the United States has in the past relied on the customary international law right of transit passage to navigate international straits like the Bab al-Mandeb. See, e.g., Bureau of Oceans & Int'l Envtl. & Sci. Affairs, U.S. Dep't of State, No. 112, Limits in the Seas: United States Responses to Excessive National Maritime Claims 65–67 (Mar. 9, 1992), at https://2009-2017.state.gov/documents/organization/58381.pdf (citing Diplomatic Note No. 449, Oct. 6, 1986 from the American Embassy at Sanaa) (“[T]he Government of the Yemen Arab Republic may not legally condition the exercise of the right of transit passage through or over an international strait, such as Bab-el-Mandeb, upon obtaining prior permission. Transit passages is a right that may be exercised by ships of all nations … .”). According to the UN Convention on the Law of the Sea, ships exercising the right of transit passage shall “refrain from any threat or use of force against the sovereignty, territorial integrity or political independence of States bordering the strait” and shall “refrain from any activities other than those incident to their normal modes of … transit unless rendered necessary by force majeure or by distress.” United Nations Convention on the Law of the Sea, Art. 39, Dec. 10, 1982, 1833 UNTS 397. Though not party to the Convention, the United States has claimed that the “normal mode” of transit for warships exercising their right of transit passage includes activities consistent with the security of their forces. Bureau of Oceans & Int'l Envtl. & Sci. Affairs, supra at 65.

²⁸ UN Charter, Art. 2(4), 51 (allowing limited use of force in another state's territory based on the “inherent right” of self-defense).

²⁹ Letter dated 15 October 2016 from the Permanent Representative of the United States of America to the United Nations addressed to the President of the Security Council, UN Doc. S/2016/869 (Oct. 15, 2016) [hereinafter Letter from Samantha Power].

³⁰ White House Press Release, supra note 2; Report on the Legal and Policy Frameworks Guiding the United States’ Use of Military Force and Related National Security Operations 18 (Dec. 2016), available at https:// www.documentcloud.org/documents/3232529-Framework-Report-Final.html#document/p4 [hereinafter Report Guiding the Use of Force] (stating that “U.S. support for the Saudi-led coalition … is being provided in the context of the Coalition's military operations being undertaken in response to the Government of Yemen's request for assistance, including military support, to protect the sovereignty, peace, and security of Yemen”). Claims about Yemen's consent are complicated by the fact that the constitutionally elected president, President Abdo Rabbo Mansour Hadi, was exiled in 2014 after the Houthi rebels and loyalists to former President Ali Abdullah Saleh seized the capital city of Sana'a. U.S. Dep't of State, 2015 Country Reports on Human Rights Practices: Yemen (Apr. 13, 2016), at https://2009-2017.state.gov/j/drl/rls/hrrpt/2015/nea/252955.htm; see also Moorehead, Alex, Yemen's Consent for U.S. Counterterrorism Operations: Questions for the Trump Administration, Just Security (Feb. 9, 2017)Google Scholar, at https://www.justsecurity.org/37530/yemens-consent-u-s-counterterrorism-operations-questions-trump-administration (discussing the uncertainty about the legal validity of consent by the Hadi administration). The United States has not publicly questioned the legitimacy of the exiled government's consent, though the recent White House Report acknowledged general challenges in seeking consent from “countries where governments are rapidly changing [or] have lost control of significant parts of their territory… .” See Report Guiding the Use of Force, supra at 30.

³¹ See Letter from Samantha Power, supra note 29.

³² U.S. Dep't of State Special Briefing, supra note 21.

³³ U.S. Dep't of Defense News Transcript, supra note 24.

³⁴ U.S. Dep't of State Special Briefing, supra note 21.

³⁵ Id.

³⁶ Yemen Denies Targeting U.S. Warship, Saba News Agency (Yemen) (Oct. 13, 2016), at https:// www.sabanews.net/en/news443542.htm.

³⁷ U.S. Dep't of State Special Briefing, supra note 21.

³⁸ Id.

³⁹ Lamothe, supra note 17.

⁴⁰ UN Human Rights Office of the High Comm'r, Outrageous Attack on Funeral Makes International Investigation into Yemen Even More Vital – Zeid, OHCHR (Oct. 10, 2016), at http://www.ohchr.org/EN/NewsEvents/Pages/DisplayNews.aspx?NewsID=20662&LangID=E.

⁴¹ Id.

⁴² Id.

⁴³ Yemen: Saudi-Led Funeral Attack Apparent War Crime: Credible International Investigation Urgently Needed, Human Rights Watch (Oct. 13, 2016)Google Scholar, at https://www.hrw.org/news/2016/10/13/yemen-saudi-led-funeral-attack-apparent-war-crime.

⁴⁴ White House Press Release, Statement by NSC Spokesperson Ned Price on Yemen (Oct. 8, 2016), at https://obamawhitehouse.archives.gov/the-press-office/2016/10/08/statement-nsc-spokesperson-ned-price-yemen.

⁴⁵ See Coalition to Probe Yemen Raid that Killed 140, Al Arabiya (Saudi Arabia) (Oct. 9, 2016)Google Scholar, at https://english.alarabiya.net/en/News/middle-east/2016/10/08/Saudi-denies-Yemeni-funeral-bombing.html (quoting coalition sources denying involvement).

⁴⁶ Letter from Abdallah Al-Mouallimi, Permanent Representative of Saudi Arabia to the United Nations, to the President of the United Nations Security Council (Oct. 11, 2016), UN Doc. S/2016/850 [hereinafter Saudi Letter to UN].

⁴⁷ Press Statement by the Joint Incidents Assessment Team (JIAT) on the Great Hall Incident in Sana'a, Saudi Press Agency (Oct. 15, 2016)Google Scholar, at http://www.spa.gov.sa/1548647.

⁴⁸ Id.

⁴⁹ See, e.g., Amnesty International Response to the Saudi Arabia-Led Coalition's Investigations, Amnesty Int'l (Jan. 16, 2017)Google Scholar, at https://www.amnesty.nl/actueel/amnesty-international-response-saudi-arabia-led-coalitions-investigations; Letter to Saudi-Led Coalition Joint Incidents Assessment Team Regarding Yemen Investigations, Human Rights Watch (Jan. 13, 2017), at https://www.hrw.org/news/2017/01/16/letter-saudi-led-coalition-joint-incidents-assessment-team-regarding-yemen. For JIAT's findings on other challenged coalition attacks, see Joint Incidents Assessment Team (JIAT) on Yemen Responds to Claims on Coalition Forces’ Violations in Decisive Storm Operations, Saudi Press Agency (Aug. 5, 2016)Google Scholar, at http://www.spa.gov.sa/viewstory.php?lang=en&newsid=1524799.

⁵⁰ See U.S. Dep't of State Press Statement, Announcement of Cessation of Hostilities in Yemen (Oct. 18, 2016), at https://2009-2017.state.gov/secretary/remarks/2016/10/263252.htm (welcoming a seventy-two-hour cease-fire beginning on October 19, 2016); U.S. Dep't of State Press Statement, On the Cessation of Hostilities in Yemen (Nov. 20, 2016), at https://2009-2017.state.gov/secretary/remarks/2016/11/264466.htm (welcoming the renewal of a forty-eight-hour cease-fire that began on November 19, 2016).

⁵¹ E.g., Ben Hubbard, U.S. Fingerprints on Attacks Obliterating Yemen's Economy, N.Y. Times (Nov. 13, 2016), at https:// www.nytimes.com/2016/11/14/world/middleeast/yemen-saudi-bombing-houthis-hunger.html (enumerating various civilian targets attacked by the coalition—including hospitals, schools, bridges, power stations, poultry farms, seaports, factories, weddings, and funerals—and concluding that “hitting Yemen's economy is part of the coalition's strategy”); Bombing Businesses: Saudi Coalition Airstrikes on Yemen's Civilian Economic Structures, Human Rights Watch (July 10, 2016), at https://www.hrw.org/report/2016/07/10/bombing-businesses/saudi-coalition-airstrikes-yemens-civilian-economic-structures (documenting attacks on “civilian economic structures” from March 2015 through February 2016).

⁵² Ben Hubbard, Airstrikes by Saudi-Led Coalition Kill Dozens in Western Yemen, N.Y. Times (Oct. 30, 2016), at https:// www.nytimes.com/2016/10/31/world/middleeast/airstrikes-kill-dozens-in-western-yemen.html; Sudarsan Raghavan, Airstrikes Kill More Than 40 and Wound Scores in Yemeni Port City, Wash. Post (Oct. 31, 2016), at https://www.washingtonpost.com/world/airstrikes-kill-more-than-40-and-wound-scores-in-yemeni-port-city/2016/10/30/4666dbfd-afa3-4f8f-9542-7ad77664d4ee_story.html.

⁵³ E.g., Yemen: US-Made Bombs Used in Unlawful Airstrikes, Human Rights Watch (Dec. 8, 2016)Google Scholar, at https://www.hrw.org/news/2016/12/08/yemen-us-made-bombs-used-unlawful-airstrikes.

⁵⁴ Raghavan, supra note 52.

⁵⁵ Missy Ryan, With Small Changes, U.S. Maintains Military Aid to Saudi Arabia Despite Rebukes over Yemen Carnage, Wash. Post (Dec. 13, 2016), at https://www.washingtonpost.com/news/checkpoint/wp/2016/12/13/with-small-changes-u-s-maintains-military-aid-to-saudi-arabia-despite-rebukes-over-yemen-carnage.

⁵⁶ Id.

⁵⁷ White House Press Release, Press Briefing by Press Secretary Josh Earnest and Special Envoy for the Global Coalition to Counter ISIL, Brett McGurk (Dec. 13, 2016), at https://obamawhitehouse.archives.gov/the-press-office/2016/12/13/press-briefing-press-secretary-josh-earnest-and-special-envoy-global.

⁵⁸ Helene Cooper, U.S. Blocks Arms Sale to Saudi Arabia Amid Concerns over Yemen War, N.Y. Times (Dec. 13, 2016), at https:// www.nytimes.com/2016/12/13/us/politics/saudi-arabia-arms-sale-yemen-war.html. When asked for details, a State Department spokesman refused to discuss pending arms sales. U.S. Dep't of State Press Release, Daily Press Briefing (Dec. 13, 2016), at https://2009-2017.state.gov/r/pa/prs/dpb/2016/12/265200.htm.

⁵⁹ Hudson, John, Exclusive: White House Blocks Transfer of Cluster Bombs to Saudi Arabia, Foreign Policy (May 27, 2016)Google Scholar, at http://foreignpolicy.com/2016/05/27/exclusive-white-house-blocks-transfer-of-cluster-bombs-to-saudi-arabia/.

⁶⁰ See, e.g., Cooper, supra note 58 (“The absence of a more comprehensive ban, given the ongoing unlawful strikes and the potential U.S. complicity, is deeply concerning.”) (quoting the Washington director of Human Rights Watch).

⁶¹ U.S. Dep't of State Press Release, Daily Press Briefing (Dec. 9, 2016), at https://2009-2017.state.gov/r/pa/prs/dpb/2016/12/265016.htm (confirming approval of military sales to Saudi Arabia worth $3.5 billion, mostly for Chinook helicopters not intended for combat roles).

⁶² See H.R.J. Res. 98, 114th Cong. (2016); S.J. Res. 32, 114th Cong. (2016).

⁶³ Letter from Sarah Margon, Washington Director of Human Rights Watch, to Barack Obama, President of the United States (Oct. 31, 2016), available at https://www.hrw.org/sites/default/files/supporting_resources/review_of_the_armed_conflict_in_yemen_letter_to_president_obama_english.pdf [hereinafter HRW Letter]; Yemen: US-Made Bombs Used in Unlawful Airstrikes, Human Rights Watch (Dec. 8, 2016), at https:// www.hrw.org/news/2016/12/08/yemen-us-made-bombs-used-unlawful-airstrikes.

⁶⁴ HRW Letter, supra note 63.

⁶⁵ Senator Rand Paul (R-Ky.) reportedly said “[w]e are complicit and actively involved with war in Yemen,” yet “[there has] been no debate in Congress … over whether or not we should be at war in Yemen.” Rosenberg & Mazzetti, supra note 5. Senator Ted Lieu (D-Calif.) reportedly asked: “Why would we be refueling a jet carrying bombs if we don't know what target it's about to strike? If we just refueled a jet that is hitting a hospital, that's a problem.” Ryan, supra note 6.

⁶⁶ U.S. Dep't of State Press Release, Daily Press Briefing, supra note 61.

⁶⁷ See U.S. Dep't of State Press Release, Special Briefing, supra note 21.

⁶⁸ Ryan, supra note 6.

⁶⁹ Id.

⁷⁰ See Final Rep. of the Panel of Experts on Yemen, at 3, transmitted by Letter Dated 27 January 2017 from the Panel of Experts on Yemen Addressed to President of the Security Council, UN Doc. S/2017/81 (2017).

⁷¹ E.g., Goodman, Ryan & Jackson, Miles, State Responsibility for Assistance to Foreign Forces (aka How to Assess US-UK Support for Saudi Ops in Yemen), Just Security (Aug. 31, 2016)Google Scholar, at https://www.justsecurity.org/32628/state-responsibility-assistance-foreign-forces-a-k-a-assess-us-uk-support-saudi-military-ops-yemen; Schaack, Beth Van, Evaluating Proportionality and Long-Term Civilian Harm Under the Laws of War, Just Security (Aug. 29, 2016)Google Scholar, at https:// www.justsecurity.org/32577/evaluating-proportionality-long-term-civilian-harm-law-war.

⁷² Int'l Law Comm'n, Draft Articles on Responsibility of States for Internationally Wrongful Acts, with Commentaries, Art. 16 (2001). The text of Article 16 states only that the aid or assistance must be provided “with knowledge of the circumstances of the internationally wrongful act”; however, the Commentaries attached to the Draft Articles explain this limitation in part as requiring that the aid or assistance be provided “with a view to facilitating the commission of that act.” Id. at cmt. 3. Commentators have noted and challenged the role of the Commentaries in substantially limiting this element of Article 16. See, e.g., Bodansky, Daniel & Crook, John R., Symposium: The ILC's State Responsibility Articles, 96 AJIL 733, 789 (2002)Google Scholar. See infra notes 77–79 and corresponding text for further discussion of Article 16.

⁷³ E.g., Moynihan, Harriet, State Complicity in Other States’ Bad Acts—and How to Avoid It, Just Security (Nov. 14, 2016)Google Scholar, at https:// www.justsecurity.org/34379/state-complicity-states-bad-acts-and-avoid-2; Weizmann, Nathalie, Are the U.S. and U.K. Parties to the Saudi-led Armed Conflict Against the Houthis in Yemen?, Just Security (Sept. 22, 2016)Google Scholar, at https:// www.justsecurity.org/33095/u-s-u-k-parties-saudi-led-armed-conflict-houthis-yemen.

⁷⁴ E.g., Goodman, Ryan, The Law of Aiding and Abetting (Alleged) War Crimes: How to Assess US and UK Support for Saudi Strikes in Yemen, Just Security (Sept. 1, 2016)Google Scholar, at https://www.justsecurity.org/32656/law-aiding-abetting-alleged-war-crimes-assess-uk-support-saudi-strikes-yemen.

⁷⁵ Against this backdrop, Reuters published an October 10, 2016, article detailing previously undisclosed material (obtained through the Freedom of Information Act) that illustrated U.S. officials’ debates—spanning from mid-May 2015 to February 2016—as to whether the United States qualified as a “co-belligerent” in the Yemen war and whether the United States could be exposed to allegations of LOAC violations. See Strobel, Warren & Landay, Jonathan, Exclusive: As Saudis Bombed Yemen, U.S. Worried About Legal Blowback, Reuters (Oct. 10, 2016)Google Scholar, at http://uk.reuters.com/article/uk-usa-saudi-yemen-exclusive-idUKKCN12A0BG. These internal debates do not appear ever to have been discussed publicly.

⁷⁶ See Report Guiding the Use of Force, supra note 30, at 14.

⁷⁷ Compare Int'l Law Comm'n, supra note 72, with Report Guiding the Use of Force, supra note 30, at 14.

⁷⁸ Int'l Law Comm'n, supra note 72, at cmt. 5; Report Guiding the Use of Force, supra note 30, at 14.

⁷⁹ White House Press Release, Readout of the President's Call with King Salman bin Abd Al-Aziz Al Saud of Saudi Arabia (Jan. 29, 2017), at https://www.whitehouse.gov/the-press-office/2017/01/29/readout-presidents-call-king-salman-bin-abd-al-aziz-al-saud-saudi-arabia.