In 1980, the Fourth Circuit decided United States v. Truong, another criminal prosecution that arose out of the defendant’s spying on behalf of the Socialist Republic of Vietnam. The case squarely presented the issue of the executive branch’s inherent power to conduct warrantless surveillance for national security purposes:
The defendants raise a substantial challenge to their convictions by arguing that the surveillance conducted by the FBI violated the Fourth Amendment and that all the evidence uncovered through that surveillance must consequently be suppressed. As has been stated, the government did not seek a warrant for the eavesdropping on Truong’s phone conversations or the bugging of his apartment. Instead, it relied upon a “foreign intelligence” exception to the Fourth Amendment’s warrant requirement. In the area of foreign intelligence, the government contends, the President may authorize surveillance without seeking a judicial warrant because of his constitutional prerogatives in the area of foreign affairs
The court agreed with the government’s position:
For several reasons, the needs of the executive are so compelling in the area of foreign intelligence, unlike the area of domestic security, that a uniform warrant requirement would, following [United States v. United States District Court, 407 U.S. 297 (1972)], “unduly frustrate” the President in carrying out his foreign affairs responsibilities. First of all, attempts to counter foreign threats to the national security require the utmost stealth, speed and secrecy. A warrant requirement would add a procedural hurdle that would reduce the flexibility of executive foreign intelligence activities, in some cases delay executive response to foreign intelligence threats, and increase the chance of leaks regarding sensitive executive operations.
