For helpful comments and suggestions, we thank Kathy Bradley, Jean Galbraith, Oona Hathaway, Rebecca Ingber, Marty Lederman, Eric Posner, Michael Ramsey, Stephen Vladeck, and Matthew Waxman. For research assistance, we thank Ahson Azmat, Jenya Godina, Noah Heinz, Alexa Kissinger, Emma Kohse, and Luca Marzorati.

1 James R. Clapper, Director of National Intelligence, Statement for the Record Before the U.S. Senate Armed Services Committee: Worldwide Threat Assessment of the U.S. Intelligence Community 4 (Feb. 9, 2016), available at https://www.armed-services.senate.gov/imo/media/doc/Clapper_02-09-16.pdf.

2 Authorization for Use of Military Force, Pub. L. No. 107-40, 115 Stat. 224 (2001).

3 See Abramowitz, David, The President, the Congress, and Use of Force: Legal and Political Considerations in Authorizing Use of Force Against International Terrorism, 43 Harv. Int’l L.J. 71, 73 (2002)Google Scholar.

4 See Military Order of November 13, 2001, Detention, Treatment, and Trial of Certain Non-citizens in the War Against Terrorism, 66 Fed. Reg. 57,831 (Nov. 13, 2001).

5 See U.S. Department of Justice, Legal Authorities Supporting the Activities of the National Security Agency Described by the President (Jan. 19, 2006), available at https://epic.org/privacy/terrorism/fisa/doj11906wp.pdf.

6 See, e.g., Brief for the Respondent-Appellee at 21, Al-Marri v. Wright, 487 F.3d 160 (4th Cir. 2007) (No. 06-7427), available at http://www.brennancenter.org/sites/default/files/legacy/d/download_file_47460.pdf.

7 See Bradley, Curtis A. & Goldsmith, Jack L., Congressional Authorization and the War on Terrorism, 118 Harv. L. Rev. 2047, 2066–72, 2107–33 (2005)Google Scholar (describing some of the debates).

8 Hamdi v. Rumsfeld, 542 U.S. 507 (2004). This holding emerged from a combination of Justice O’Connor's plurality opinion for four justices, and Justice Thomas's dissent. See id. at 579 (Thomas, J., dissenting) (arguing that Hamdi's “detention falls squarely within the Federal Government's war powers”). A different majority of the Court ruled that the Due Process Clause required the government to permit Hamdi to challenge the factual basis for his detention before a neutral decision maker. See id. at 553 (Souter, J., concurring in part, dissenting in part, and concurring in the judgment).

9 Id. at 518.

10 See infra note 61.

11 Hamdan v. Rumsfeld, 548 U.S. 557, 594 (2006) (citation omitted).

12 See Boumediene v. Bush, 553 U.S. 723 (2008) (holding that the Constitution's Suspension Clause applies to the detention of noncitizens at Guantánamo Bay); Rasul v. Bush, 542 U.S. 466 (2004) (holding that the federal habeas statute, 28 U.S.C. §2241, conferred jurisdiction to determine the legality of military detention at Guantánamo); Rumsfeld v. Padilla, 542 U.S. 426 (2004) (dismissing on jurisdictional grounds a habeas petition filed by a U.S. citizen captured and detained on U.S. soil).

13 See, e.g., Al-Marri v. Pucciarelli, 534 F.3d 213 (4th Cir. 2008) (en banc), vacated sub nom. Al-Marri v. Spagone, 555 U.S. 1220 (2009); Padilla v. Hanft, 423 F.3d 386 (4th Cir. 2005), cert. denied, 547 U.S. 1062 (2006). In addition, one district court held that the AUMF did not authorize the president to conduct warrantless electronic surveillance, ACLU v. NSA, 438 F.Supp.2d 754, 780 (E.D. Mich. 2006), but the Sixth Circuit vacated the order on standing grounds, ACLU v. NSA, 493 F.3d 644, 656 (6th Cir. 2007).

14 Boumediene, 553 U.S. 723. Habeas cases from Guantánamo had as a practical matter been consolidated in federal courts in the District of Columbia since 2004. See Vladeck, Stephen I., The D.C. Circuit After Boumediene, 41 Seton Hall L. Rev. 1451, 1452 (2011)Google Scholar.

15 Boumediene v. Bush, 583 F.Supp.2d 133, 135 (D.D.C. 2008). During the period between Boumediene and President Obama's inauguration, district court judges in the District of Columbia relied on and applied this standard as the one “previously adopted by this Court in the Boumediene cases.” See, e.g., El Gharani v. Bush, 593 F.Supp.2d 144, 147 (D.D.C. 2008).

16 See, e.g., Sliti v. Bush, 592 F.Supp.2d 46 (D.D.C. 2008); El Gharani, 593 F.Supp.2d 144; Al Alwi v. Bush, 593 F.Supp.2d 24 (D.D.C. 2008); Ahmed v. Bush, 585 F.Supp.2d 127 (D.D.C. 2008).

17 See Exec. Order 13,492, Review and Disposition of Individuals Detained at the Guantánamo Bay Naval Base and Closure of Guantánamo Detention Facilities, 74 Fed. Reg. 4897 (Jan. 22, 2009), at https://www.whitehouse.gov/the_press_office/ClosureOfGuantanamoDetentionFacilities. The president ordered CIA detention sites to be closed immediately. Ensuring Lawful Interrogations, Exec. Order 13,491, 74 Fed. Reg. 4893 (Jan. 22, 2009), at https://www.whitehouse.gov/the_press_office/EnsuringLawfulInterrogations.

18 White House Press Release, Remarks by the President on National Security (May 21, 2009), at https://www.whitehouse.gov/the-press-office/remarks-president-national-security-5-21-09.

19 Respondents’ Memorandum Regarding the Government's Detention Authority Relative to Detainees Held at Guantánamo Bay at 1, In re Guantánamo Bay Detainee Litigation (D.D.C. Mar. 13, 2009) (Misc. No. 08-442) [hereinafter March 2009 Brief], available at https://www.justice.gov/sites/default/files/opa/legacy/2009/03/13/memo-re-det-auth.pdf.

20 Id. at 2.

21 See also id. at 3 (“The United States can lawfully detain persons currently being held at Guantánamo Bay who were ‘part of,’ or who provided ‘substantial support’ to, al-Qaida or Taliban forces and ‘associated forces.’ This authority is derived from the AUMF, which empowers the president to use all necessary and appropriate force to prosecute the war, in light of law-of-war principles that inform the understanding of what is ‘necessary and appropriate.’”).

22 Id. at 7.

23 Boumediene, 553 U.S. at 798 (“[O]ur opinion does not address the content of the law that governs petitioners’ detention.”).

24 See Azmy, Baher, Executive Detention, Boumediene, and the New Common Law of Habeas, 95 Iowa L. Rev. 445 (2010)Google Scholar.

25 See, e.g., Latif v. Obama, 677 F.3d 1175, 1183 (D.C. Cir. 2012) (ruling that a court could consider hearsay evidence in determining whether an individual qualified for detention and that official government records and reports were subject to a “presumption of regularity”).

26 See, e.g., Khan v. Obama, 655 F.3d 20, 23 (D.C. Cir. 2011); Barhoumi v. Obama, 609 F.3d 416, 432 (D.C. Cir. 2010).

27 See, e.g., Bensayah v. Obama, 610 F.3d 718, 725 (D.C. Cir. 2010); Hamlily v. Obama, 616 F.Supp.2d 63, 75 (D.D.C. 2009); see also Bradley & Goldsmith, supra note 7, at 2111–13 (arguing for functional approach to the issue).

28 March 2009 Brief, supra note 19, at 2. For a detailed description of how courts applied this functional approach in practice, see Benjamin Wittes, Robert M. Chesney, Larkin Reynolds & The Harvard Law School National Security Research Committee, The Emerging Law of Detention 2.0: The Guantánamohabeascases as Law Making 1 (2012), available at http://www.brookings.edu//media/research/files/reports/2011/5/guantanamo-wittes/chesney-full-text-update32913.pdf.

29 See Al-Maqaleh v. Hagel, 738 F.3d 312 (D.C. Cir. 2013); Al-Maqaleh v. Gates, 605 F.3d 84 (D.C. Cir. 2010).

30 Al-Bihani v. Obama, 590 F.3d 866, 874 (D.C. Cir. 2010); see also Al-Maqaleh,, 738 F.3d at 330 (“Whether an armed conf lict has ended is a question left exclusively to the political branches.”).

31 See Razak v. Obama, 2016 U.S. Dist. LEXIS 41034 (D.D.C. 2016); Al Warafi v. Obama, 2015 U.S. Dist. LEXIS 99781 (D.D.C. 2015); Al Odah v. United States, 62 F.Supp.3d 101 (D.D.C. 2014).

32 See Al-Aulaqi v. Obama, 727 F.Supp.2d 1 (D.D.C. 2010); see also Al-Aulaqi v. Panetta, 35 F.Supp.3d 56 (D.D.C. 2014) (dismissing wrongful death suit).

33 See National Defense Authorization Act for Fiscal Year 2012, Pub. L. No. 112-81, sec. 1021(b)(2), 125 Stat. 1298, 1562 (2011) (codified at 10 U.S.C. §801).

34 See Report of the Committee on Armed Services, National Defense Authorization Act for Fiscal Year 2012, H.R. Rep. No. 112-78, sec. 1034, at 209 (May 17, 2011) (“The committee supports the Executive Branch's interpretation of the Authorization for Use of Military Force, as it was described in a March 13, 2009, filing before the U.S. District Court for the District of Columbia.”).

35 Stephen W. Preston, General Counsel, U.S. Department of Defense, The Legal Framework for the United States’ Use of Military Force Since 9/11 (Apr. 10, 2015), at http://www.defense.gov/News/Speeches/Speech-View/Article/606662/the-legal-framework-for-the-united-states-use-of-military-force-since-911.

36 March 2009 Brief, supra note 19, at 2.

37 See Charlie Savage, Power Wars: Inside Obama's Post-9/11 Presidency 120, 295, 487 (2015) (basing this conclusion on interviews and internal government documents).

38 See Periodic Review of Individuals Detained at Guantánamo Bay Naval Station Pursuant to the Authorization for Use of Military Force, Exec. Order 13,567, 76 Fed. Reg. 13277 (Mar. 7, 2011), at https://www.whitehouse.gov/the-press-office/2011/03/07/executive-order-13567-periodic-review-individuals-detained-guant-namo-ba.

39 See, e.g., Preston, supra note 35 (describing “the groups and individuals against which the U.S. military was taking direct action (that is, capture or lethal operations) under the authority of the 2001 AUMF, including associated forces”).

40 See George W. Bush, Letter to Congressional Leaders on Reporting on the Deployments of United States Combat-Equipped Armed Forces Around the World, 2 Pub. Papers 1469 (Dec. 16, 2008), available at https://www.gpo.gov/fdsys/pkg/PPP-2008-book2/pdf/PPP-2008-book2-doc-pg1469.pdf.

41 As of April 2016, Obama had ordered approximately ten times as many drone strikes as Bush, which had killed seven times as many people. See Micah Zenko, Obama's Embrace of Drone Strikes Will Be a Lasting Legacy, N.Y. Times (Jan. 12, 2016), at http://www.nytimes.com/roomfordebate/2016/01/12/reflecting-on-obamas-presidency/obamas-embrace-of-drone-strikes-will-be-a-lasting-legacy (noting that ratios are based on average estimates provided by three nongovernmental organizations).

42 See Savage, supra note 37, at 224–27, 274–79, 686; see also Charlie Savage, Is the U.S. Now at War with Shabab? Not Exactly, N.Y. Times, Mar. 15, 2016, at A11.

43 See Exec. Order 13,732, United States Policy on Pre- and Post-strike Measures to Address Civilian Casualties in U.S. Operations Involving the Use of Force, 81 Fed. Reg. 44485 (July 1, 2016), at https://www.whitehouse.gov/the-press-office/2016/07/01/executive-order-united-states-policy-pre-and-post-strike-measures; White House Press Release, Fact Sheet: U.S. Policy Standards and Procedures for the Use of Force in Counterterrorism Operations Outside the United States and Areas of Active Hostilities (May 23, 2013) [hereinafter U.S. Policy Standards and Procedures], available at https://www.whitehouse.gov/sites/default/files/uploads/2013.05.23_fact_sheet_on_ppg.pdf; White House Memorandum, Presidential Policy Guidance: Procedures for Approving Direct Action Against Terrorist Targets Located Outside the United States and Areas of Active Hostilities (May 22, 2013), at https://www.aclu.org/other/presidential-policy-guidance.

44 Jeh C. Johnson, General Counsel, Department of Defense, Speech at the Oxford Union: The Conflict Against Al Qaeda and Its Affiliates: How Will It End (Nov. 30, 2012), available at http://www.state.gov/documents/organization/211954.pdf.

45 Id. at 7–8.

46 White House Press Release, Remarks of President Barack Obama at the National Defense University (May 23, 2013), at https://www.whitehouse.gov/the-press-office/2013/05/23/remarks-president-barack-obama.

47 See, e.g., Clapper, supra note 1; John O. Brennan, Director of the Central Intelligence Agency, Statement Before the U.S. Senate Select Committee on Intelligence (June 16, 2016), available at http://www.intelligence.senate.gov/sites/default/files/documents/jobrennanstatement.pdf.

48 Clapper, supra note 1; Interview by Al Arabiya with CIA Director John O. Brennan, Director of the Central Intelligence Agency (June 12, 2016), at http://english.alarabiya.net/en/perspective/features/2016/06/12/Full-transcript-of-Al-Arabiya-s-interview-with-CIA-chief-John-Brennan.html.

49 See White House Press Release, Statement by the President on the End of the Combat Mission in Afghanistan (Dec. 28, 2014), at https://www.whitehouse.gov/the-press-office/2014/12/28/statement-president-end-combat-mission-afghanistan.

50 See Mark Landler, Obama Says He Will Keep More Troops in Afghanistan Than Planned, N.Y. Times, July 7, 2016, at A8.

51 See Savage, supra note 37, at 688–89; see also Charlie Savage, White House Invites Congress to Approve ISIS Strikes, but Says It Isn't Necessary, N.Y. Times, Sept. 11, 2014, at A10.

52 Patricia Zengerle & Jonathan Landay, CIA Director Says Islamic State Still Serious Threat, REUTERS, June 16, 2016, at http://af.reuters.com/article/worldNews/idAFKCN0Z21OA.

53 Preston, supra note 35.

54 See, e.g., Aaron Mehta, Odierno: ISIS Fight Will Last 10 to 20 Years, Defense News, July 17, 2015, at 3; Dan De Luce, Is the U.S. Ready for an Endless War Against the Islamic State?, Foreign Pol’y (Aug. 27, 2015), at http://foreignpolicy.com/2015/08/27/is-the-u-s-ready-for-an-endless-war-against-the-islamic-state.

55 See Draft Joint Resolution to Authorize the Limited Use of the United States Armed Forces Against the Islamic State of Iraq and the Levant (2014), available at https://www.whitehouse.gov/sites/default/files/docs/aumf_02112015.pdf.

56 White House Press Release, Letter from the President—Authorization for the Use of United States Armed Forces in Connection with the Islamic State of Iraq and the Levant (Feb. 11, 2015), at https://www.whitehouse.gov/the-press-office/2015/02/11/letter-president-authorization-use-united-states-armed-forces-connection.

57 See Defendant's Motion to Dismiss at 2, Smith v. Obama, No. 16-843 (D.D.C. 2016) available at https://www.documentcloud.org/documents/2991414-Smith-v-Obama-Govt-Motion-to-Dismiss.html. But cf. War Powers Resolution, Pub. L. No. 93-148, sec. 8(a), 87 Stat. 555 (1973) (codified at 50 U.S.C. §§1541–1548 (2012)) (“Authority to introduce United States Armed Forces into hostilities … shall not be inferred—(1) from … any provision contained in any appropriation Act, unless such provision specifically authorizes the introduction of United States Armed Forces into hostilities … andstating that it is intended to constitute specific statutory authorization within the meaning of this [joint resolution].”).

58 See Complaint for Declaratory Relief, Smith, Case No. 16-843, available at https://assets.documentcloud.org/documents/2823282/Smith-Complaint-as-Filed.pdf.

59 In its motion to dismiss, the Obama administration invoked the political question doctrine, limitations on standing, and sovereign immunity. See Defendant's Motion to Dismiss, Smith v. Obama, supra note 57. For analysis, see Marty Lederman, DOJ's Motion to Dismiss in Smith v. Obama, The Case Challenging the Legality of the War Against ISIL, Just Security (July 14, 2016), at https://www.justsecurity.org/31984/dojs-motion-dismiss-smith-v-obama-case-challenging-legality-war-isil.

60 See, e.g., Eric H. Holder, Attorney General, U.S. Department of Justice, Speech at the Northwestern University School of Law (Mar. 5, 2012), at https://www.justice.gov/opa/speech/attorney-general-eric-holder-speaks-northwestern-university-school-law (“International legal principles, including respect for another nation's sovereignty, constrain our ability to act unilaterally.”); Jeh Charles Johnson, National Security Law, Lawyers, and Lawyering in the Obama Administration, 31 Yale L. & Pol’y Rev. 141, 147 (2012) (“International legal principles, including respect for a state's sovereignty and the laws of war, impose important limits on our ability to act unilaterally, and on the way in which we can use force in foreign territories.”).

61 See Hamdi, 542 U.S. at 520 (“It is a clearly established principle of the law of war that detention may last no longer than active hostilities.”) (citations omitted); id. at 521 (“[O]ur understanding [of the government's detention authority under the AUMF] is based on longstanding law-of-war principles. If the practical circumstances of a given conf lict are entirely unlike those of the conf licts that informed the development of the law of war, that understanding may unravel.”).

62 March 2009 Brief, supra note 19, at 1; see also Harold Hongju Koh, Legal Adviser, U.S. Department of State, The Obama Administration and International Law, Speech at the Annual Meeting of the American Society of International Law, Washington, D.C. (Mar. 25, 2010), at http://www.state.gov/s/l/releases/remarks/139119.htm (“[W]e are resting our detention authority on a domestic statute—the 2001 Authorization for Use of Military Force (AUMF)—as informed by the principles of the laws of war.”).

63 March 2009 Brief, supra note 19, at 1.

64 Id.

65 See id. at 6 n.2.

66 See id. at 8.

67 Id. at 9.

68 See, e.g., Nils Melzer, Interpretive Guidance on the Notion of Direct Participation in Hostilities Under International Law, 90 Int’l Rev. Red Cross 991, 1135 (2008); Ryan Goodman & Derek Jinks, International Law, U.S. War Powers, and the Global War on Terrorism, 118 Harv. L. Rev. 2653, 2657 (2005); Scott D. MacDonald, The Lawful Use of Targeted Killing in Contemporary International Humanitarian Law, 2 J. Terrorism Res. (2011), available at http://jtr.st-andrews.ac.uk/article/10.15664/jtr.232.

69 See, e.g., Khairkhwa v. Obama, 703 F.3d 547, 550 (D.C. Cir. 2012); Al-Adahi v. Obama, 613 F.3d 1102, 1103 (D.C. Cir. 2010).

70 See March 2009 Brief, supra note 19, at 2.

71 See Brief for Respondents-Appellees at 28, Barhoumi, 609 F.3d 416. In this and other briefs, the United States relied on Hamlily, 616 F.Supp.2d at 74–75, which concluded that “[a] ‘co-belligerent’ in an international armed conf lict context is a state that has become a ‘fully f ledged belligerent fighting in association with one or more belligerent powers.’” Id. at 75 (quoting Bradley & Goldsmith, supra note 7, at 2112 (quoting Morris Greenspan, The Modern Law of Land Warfare 531 (1959))); see also Johnson, supra note 60, at 146 (noting that the associated forces category “is based on the well-established concept of co-belligerency in the law of war”).

72 See Rebecca Ingber, Co-belligerency and War Powers: The Making of Executive Law, 42 Yale J. Int’l L. (forthcoming 2017); Jens David Ohlin, Targeting Co-belligerents, in Targeted Killings: Law & Morality in an Asymmetrical World 60 (Claire Finkelstein, Jens David Ohlin & Andrew Altman eds., 2011).

73 See sources cited supra note 26.

74 See Brief for Appellees at 21, Al-Bihani, 590 F.3d 866; Brief for Respondents-Appellants, Hatim v. Gates, 632 F.3d 720 (D.C. Cir. 2011) (No. 10-5048). As discussed in part II, Congress embraced the administration's position concerning both associated forces and substantial supporters in the 2012 National Defense Authorization Act.

75 See, e.g., Brief for Appellees at 12, Alsabri v. Obama, 684 F.3d 1298 (D.C. Cir. 2012) (No. 11-5081) (arguing that detainee “was ‘part of’ Al-Qaida, the Taliban, or an Associated Force”); Brief for Respondents-Appellees at 23, Al Alwi v. Obama, 653 F.3d 11 (D.C. Cir. 2011) (No. 09-5125) (arguing that detainee was “part of, or substantially support[ed], Taliban, Al-Qaida, or Associated Forces”); Brief for Respondents-Appellees at 25, Al-Bihani v. Obama, 590 F.3d 866 (D.C. Cir. 2010) (No. 09-5051) (arguing that detainee was “part of Taliban or al-Qaida forces (or associated forces)”).

76 See, e.g., Alsabri, 684 F.3d at 1302 (accepting government's triple alternate formulation); Al Alwi, 653 F.3d at 16–17 (accepting two of government's four alternative designations); Al-Bihani, 590 F.3d at 872 (accepting government's triple alternatives and, on separate grounds, adding a fourth).

77 Courts have responded to these claims in various ways, all ultimately agreeing with the Obama administration position. See supra text accompanying notes 29–32.

78 See Johnson, supra note 44 (relying on “conventional legal principles” and citing Ludecke v. Watkins, 335 U.S. 160 (1948), as “holding that the President's authority to detain German nationals continued for over six years after the fighting with Germany had ended”).

79 Exec. Order 13,567, supra note 38, sec. 1(b).

80 Al-Bihani, 590 F.3d at 871.

81 U.S. Government Response to Petition for Rehearing and Rehearing En Banc at 8, Al-Bihani, 590 F.3d 866, available at http://www.scotusblog.com/wp-content/uploads/2010/05/US-response-re-rehear-Al-Bihani-5-13-10.pdf.

82 Al-Bihani, 590 F.3d 866, reh’g, en banc, denied, 619 F.3d 1 (D.C. Cir. 2010).

83 See, e.g., Vladeck, supra note 14, at 1462–63.

84 See National Defense Authorization Act for Fiscal Year 2012, supra note 33, §§1021–1024.

85 This phenomenon is not new. See Curtis A. Bradley & Jean Galbraith, Presidential War Powers as a Two-Level Dynamic: International Law, Domestic Law, and Practice-Based Legal Change, 91 N.Y.U. L. Rev. 689 (2016) (describing how international law has historically been invoked by presidents to expand domestic war authority); see also Rebecca Ingber, International Law Constraints as Executive Power, 57 Harv. Int’l L.J. 49 (2016) (discussing how the executive branch uses international law in a variety of ways to bolster its domestic authority).

86 Koh, supra note 62.

87 Id.

88 Memorandum from Acting Assistant Attorney General David J. Barron to the Attorney General, Re: Applicability of Federal Criminal Laws and the Constitution to Contemplated Lethal Operations Against Shaykh Anwar al-Aulaqi 27 (July 16, 2010) [hereinafter Barron Memorandum] available at https://www.justice.gov/sites/default/files/olc/pages/attachments/2015/04/02/2010-07-16_-_olc_aaga_barron_-_al-aulaqi.pdf; see also White House Press Release, Remarks by President Obama at Strasbourg Town Hall, Strasbourg, France (Apr. 3, 2009), at https://www.whitehouse.gov/the-press-office/remarks-president-obama-strasbourg-town-hall; White House Press Release, John O. Brennan, Assistant to the President for Homeland Security and Counterterrorism, Remarks at Harvard Law School: Strengthening Our Security by Adhering to Our Values and Laws (Sept. 16, 2011), at https://www.whitehouse.gov/the-press-office/2011/09/16/remarks-john-o-brennan-strengthening-our-securityadhering-our-values-an(“The United States does not view our authority to use military force against al-Qa’ida as being restricted solely to ‘hot’ battlefields like Afghanistan.”).

89 See, e.g., Melzer, supra note 68, at 77; Jelena Pejic, Extraterritorial Targeting by Means of Armed Drones: Some Legal Implications, 893 Int’l Rev. Red Cross 1, 16–18, 36–37 (2015); Special Rapporteur on the Promotion and Protection of Human Rights and Fundamental Freedoms While Countering Terrorism, paras. 61–64, UN Doc. A/68/389 (Sept. 18, 2013), available at https://www.justsecurity.org/wp-content/uploads/2013/10/2013EmmersonSpecialRapporteurReportDrones.pdf.

90 See U.S. Policy Standards and Procedures, supra note 43.

91 Brian Egan, Legal Adviser, U.S. Department of State, International Law, Legal Diplomacy, and the Counter-ISIL Campaign 10 (Apr. 4, 2016), available at https://www.justsecurity.org/wp-content/uploads/2016/04/Egan-ASIL-speech.pdf.

92 See Savage, supra note 37, at 254–56; Spencer Ackerman, US to Continue “Signature Strikes” on People Suspected of Terrorist Links, Guardian (July 1, 2016), at https://www.theguardian.com/us-news/2016/jul/01/obama-continue-signature-strikes-drones-civilian-deaths.

93 See, e.g., Holder, supra note 60 (“[I]t is entirely lawful—under both United States law and applicable law of war principles—to target specific senior operational leaders of al Qaeda and associated forces.”).

94 Cf. David Pozen, The Rhetorical Presidency Meets the Drone Presidency, New Rambler (2015), at http://newramblerreview.com/book-reviews/law/the-rhetorical-presidency-meets-the-drone-presidency (“All of the constraint is lodged in abstract descriptors.”); Ashley S. Deeks, TheObamaAdministration, International Law, and Executive Minimalism, 110 AJIL 646 (2016) (noting that “the Obama administration has sometimes taken action in the face of two (or more) possible legal theories without articulating which theory it is using”).

95 See Barron Memorandum, supra note 88, at 21.

96 See Savage, supra note 37, at 274–77. Savage cites one instance in which the Pentagon general counsel invoked the outer bounds of “associated forces” to abort a strike on al-Shabaab, although he notes that the general counsel later changed his mind about the issue in light of new intelligence. See id. at 276–77.

97 See Christine Gray, International Law and the Use of Force 149 (3d ed. 2008).

98 Brennan, supra note 88; see also Egan, supra note 91; U.S. Department of Justice White Paper, Lawfulness of a Lethal Operation Directed Against a U.S. Citizen Who Is a Senior Operational Leader of Al-Qa’ida or an Associated Force (Nov. 8, 2011), available at https://fas.org/irp/eprint/doj-lethal.pdf. But see Erakat, Noura S., New Imminence in the Time of Obama: The Impact of Targeted Killings on the Law of Self-Defense, 56 Ariz. L. Rev. 195 (2014)Google Scholar (criticizing the administration's position); Christophe Paulussen & Kinga Tibori Szabó, Testing the Validity of US Self-Defence Arguments Against the Khorasan Group in Syria, Int’l CTR. Counterterrorism (Nov. 4, 2014), at http://icct.nl/publication/testing-the-validity-of-us-self-defence-arguments-against-the-khorasan-group-in-syria.

99 See Egan, supra note 91, at 4–5 (noting that “in Syria U.S. operations against ISIL are conducted in individual self-defense and the collective self-defense of Iraq”) (emphasis added); see also Marty Lederman, The Egan Speech and the Bush Doctrine: Imminence, Necessity, and “First Use” in the Jus ad Bellum, Just Security (Apr. 11, 2016), at https://www.justsecurity.org/30522/egan-speech-bush-doctrine-imminence-necessity-first-use-jus-ad-bellum (explaining that the United States argued in the alternative for individual self-defense “even though in recent years [the Islamic State] has not yet engaged in an armed attack specifically against the United States”).

100 See, e.g., U.S. Department of Defense News Transcript, Department of Defense Press Briefing by Rear Adm. Kirby in the Pentagon Briefing Room (Feb. 3, 2015), at http://www.defense.gov/News/News-Transcripts/Article/607008 (acknowledging that the Pentagon could not “pin down” whether attack would happen within “a day or month or week or six months,” but concluding that it “doesn't matter” because of aim to “get to the left of any boom to prevent the planning from going any further”); Scott Pelley, FBI Director on Threat of ISIS, Cybercrime, 60 Minutes (Oct. 5, 2014), at http://www.cbsnews.com/news/fbi-director-james-comey-on-threat-of-isis-cybercrime (quoting FBI Director James Comey as saying, “I can't sit here and tell you whether [Khorasan’s] plan is tomorrow or three weeks or three months from now.”).

101 See, e.g., Corten, Olivier, The “Unwilling or Unable” Test: Has It Been, and Could It Be, Accepted?, 29 Leiden J. Int’l L. 777 (2016)CrossRefGoogle Scholar; see also Goldsmith, Jack, The Contributions of the Obama Administration to the Practice and Theory of International Law, 57 Harv. Int’l L.J. 1, 8 (2016)Google Scholar (describing Obama administration's efforts to forge consensus around “unwilling or unable” test).