The Legality of Striking Syria

President Donald Trump’s decision to strike Syrian military airfields marks a considerable escalation of U.S. involvement in the now six-year Syrian Civil War. The strikes represent the first direct U.S. military action against the Assad regime, as previous U.S. military operations in Syria had targeted the Islamic State.

Q1: On what domestic legal basis were the strikes authorized?

According to the Washington Post , the president relied upon his Article II Commander-in-Chief powers. The Constitution grants Congress the authority to “declare war” but has also been interpreted to justify limited unilateral executive uses of force. As the framers’ intention was to provide the executive branch with sufficient inherent powers to defend the nation in crises, legal precedent suggests Commander-in-Chief powers authorize the use of force in self-defense of the nation and U.S. nationals abroad.

Built upon this foundational premise, the executive branch Office of Legal Counsel (OLC) has offered interpretations across administrations to justify the use of force abroad without a congressional mandate. President Obama’s 2011 Libya operation is the most notable recent case as arguably the broadest assertion of independent presidential war powers yet. The OLC opinion argued that the unilateral use of force was justified on the grounds that national interests were at stake and military operations would be limited in time and scope, not warranting an authorization for the use of military force (AUMF). Yet the concept of a “national interest” is so ambiguous and potentially elastic that this opinion offers minimal restrictions on unilateral presidential war-making.

In the case of U.S. strikes on Syrian airfields this week, the administration released talking points offering several national interests that warranted military action, including “promoting regional stability, discouraging the use of chemical weapons, and protecting a civilian population from humanitarian atrocities.”

Q2: On what international legal basis were the strikes authorized?

The administration has yet to clarify the international legal rationale for the strike. In the absence of a United Nations Security Council authorization, states are sanctioned to initiate the use of force in “ individual or collective self-defence ” under Article 51 of the U.N. Charter. Since the chemical weapons employed by Syrian armed forces did not target U.S. forces or property to warrant a response in self-defense, the U.S. military strikes seem to be in tension with that principle. Further, it is unclear whether the use of chemical weapons upon one’s own population would justify a legitimate invocation of collective self-defense. It will therefore be crucial to see what legal reasoning the Trump administration stakes its move on. Several legal scholars and former USG lawyers have offered potential rationales that support the legitimacy, if not the legality, of U.S. operations in Syria on humanitarian grounds or Responsibility to Protect (R2P), yet it remains a contentious issue of debate .

Q3: Is this déjà vu? Wasn’t this the attack Obama contemplated in 2013?

In September 2013, President Obama faced a similar predicament when Syrian President Bashar al-Assad’s first crossed the U.S. “redline” against the use of chemical weapons in the civil war. After initially professing determination to respond with military force, Obama, the former constitutional lawyer, instead turned to Congress for authorization. When congressional support for military intervention withered, the administration settled against the use of force. Nevertheless, the Obama administration continued to argue that it had sought congressional authorization out of due diligence, not necessity, and that the president retained inherent powers that would have legally supported the use of force. The legal rationale would have likely paralleled the administration’s argument regarding the 2011 Operation Odyssey Dawn in Libya.

Q4: How are recent strikes legally distinct from previous ones on the Islamic State in Syria?

Whereas no AUMF has yet been interpreted to justify U.S. use of force against the Assad regime, the Obama and Trump administrations have justified the campaign against the Islamic State under the 2001 AUMF. Upon initiating military operations in 2014, the original letter President Obama sent to Congress suggested operations were authorized by his Commander-in-Chief powers, but later referenced the continuing authority of the 2002 AUMF . The Obama administration eventually settled on the 2001 AUMF as the strongest legal basis for the fight against the Islamic State, even though many legal scholars still question the plausibility of its application.

Although the law was originally passed to justify targeting the terrorists directly responsible for the September 11th attacks, both political branches have incrementally expanded it in the 16 years since. In the 2012 NDAA , Congress expanded the purview of the 2001 AUMF by authorizing the detention of al-Qaeda, the Taliban and “associated forces.” Since the modern-day Islamic State descends from al-Qaeda in Iraq, former DoD General Council Stephen Preston has argued that the group meets the “associated forces” standard. The Trump administration has continued to rely on this legal interpretation for military actions against the Islamic State in Syria and Iraq.

Q5: What comes next?

In the 48 hours after the strikes, President Trump is required to notify Congress regarding U.S. military action in Syria in accordance with the War Powers Resolution (WPR), and it is likely the administration will offer a similar legal argument to the one the Obama team employed in 2011. The law requires that the president will then have 60 days to garner congressional authorization to sustain operations, before the WPR mandates a cessation of the use of force.

If Assad retaliates against yesterday’s strike by targeting U.S. military personnel in region, President Trump’s Commander-in-Chief powers and international law would clearly permit a proportional U.S. response.

If Assad chooses not to directly retaliate against U.S. armed forces but President Trump pursues further military operations against the regime, the administration would likely need a congressional authorization to avoid noncompliance with the WPR. While President Obama struggled to gain congressional support for his proposed AUMF for the Islamic State, Trump’s chances to pass an AUMF for operations against the Syrian government with a Republican-controlled House and Senate are superior.

By the same token, the legal constraints presented by the WPR and, more fundamentally, the Constitution, are not self-enforcing. As opposed to recent instances of judicial intervention to block executive actions on immigration, the courts have historically shied away from constitutional war powers debates to avoid ruling on political questions. Previous presidents, including President Obama in 2011, have also flouted compliance with the WPR by either arguing that it is an unconstitutional limitation on the executive’s Article II powers or advancing dubious legal arguments rejecting its application. In reality, the WPR is a tool Congress can wield to raise the political costs of sustained military operations conducted without the legislative consultation.

The administration may be steered toward pushing for an AUMF before engaging in continuous military operations to receive buy-in from Congress and, by extension, the American people. And passing an AUMF would disperse responsibility for the military engagement and political blowback if operations were to go awry. Beyond the political consequences of fighting a war unauthorized by Congress, there are little to no practical constraints on the Trump administration prosecuting military operations unilaterally. Congress retains the power of the purse and could chose to defund military operations in Syria, yet this is nearly unfathomable in the current political alignment.

Tacit congressional support for limited engagements against Assad without a formal authorization would be the most likely outcome in this scenario.

Colin McElhinny is a program manager and research associate in the International Security Program at CSIS, where he works on a broad range of issues including U.S. defense strategy, defense reform and public opinion on foreign policy. He is a master’s candidate at Georgetown University’s Security Studies Program and graduated summa cum laude and Phi Betta Kappa from the University of Mary Washington with a bachelor’s in economics and political science.

Critical Questions is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

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Colin McElhinny