The NSA activities are supported by the President’s well-recognized inherent constitutional authority as Commander in Chief and sole organ for the Nation in foreign affairs to conduct warrantless surveillance of enemy forces for intelligence purposes to detect and disrupt armed attacks on the United States. The President has the chief responsibility under the Constitution to protect America from attack, and the Constitution gives the President the authority necessary to fulfill that solemn responsibility. The President has made clear that he will exercise all authority available to him, consistent with the Constitution, to protect the people of the United States.

In the specific context of the current armed conflict with al Qaeda and related terrorist organizations, Congress by statute has confirmed and supplemented the President’s recognized authority under Article II of the Constitution to conduct such warrantless surveillance to prevent further catastrophic attacks on the homeland. In its first legislative response to the terrorist attacks of September 11th, Congress authorized the President to "use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks" of September 11th in order to prevent "any future acts of international terrorism against the United States." Authorization for Use of Military Force, Pub. L. No. 107-40, § 2(a), 115 Stat. 224, 224 (Sept. 18, 2001) (reported as a note to 50 U.S.C.A. § 1541) ("AUMF"). History conclusively demonstrates that warrantless communications intelligence targeted at the enemy in time of armed conflict is a traditional and fundamental incident of the use of military force authorized by the AUMF. The Supreme Court’s interpretation of the AUMF in Hamdi v. Rumsfeld, 542 U.S. 507 (2004), confirms that Congress in the AUMF gave its express approval to the military conflict against al Qaeda and its allies and thereby to the President’s use of all traditional and accepted incidents of force in this current military conflict—including warrantless electronic surveillance to intercept enemy communications both at home and abroad. This understanding of the AUMF demonstrates Congress’s support for the President’s authority to protect the Nation and, at the same time, adheres to Justice O’Connor’s admonition that "a state of war is not a blank check for the President," Hamdi, 542 U.S. at 536 (plurality opinion), particularly in view of the narrow scope of the NSA activities.

The AUMF places the President at the zenith of his powers in authorizing the NSA activities. Under the tripartite framework set forth by Justice Jackson in Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579, 635-38 (1952) (Jackson, J., concurring), Presidential authority is analyzed to determine whether the President is acting in accordance with congressional authorization (category I), whether he acts in the absence of a grant or denial of authority by Congress (category II), or whether he uses his own authority under the Constitution to take actions incompatible with congressional measures (category III). Because of the broad authorization provided in the AUMF, the President’s action here falls within category I of Justice Jackson’s framework. Accordingly, the President’s power in authorizing the NSA activities is at its height because he acted "pursuant to an express or implied authorization of Congress," and his power "includes all that he possesses in his own right plus all that Congress can delegate." Id. at 635.

[...]

CONCLUSION 

For the foregoing reasons, the President—in light of the broad authority to use military force in response to the attacks of September 11th and to prevent further catastrophic attack expressly conferred on the President by the Constitution and confirmed and supplemented by Congress in the AUMF—has legal authority to authorize the NSA to conduct the signals intelligence activities he has described. Those activities are authorized by the Constitution and by statute, and they violate neither FISA nor the Fourth Amendment.

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