The history of NSL [national security letter] powers can serve as an illuminating example of the post-Church Committee development of intelligence investigations. Many of the Church Committee findings and recommendations concerning the need for expanded oversight to prevent the executive branch from violating or ignoring the law, excessively using intrusive investigation techniques, and conducting overbroad investigations with inadequate controls on the retention and dissemination of the information gathered are all reflected in the development of NSL powers and authorities from their creation in 1978 through passage of the PlRA [USA PATRIOT Improvement and Reauthorization Act] in 2006. At each stage of this development, Congress attempted to balance civil liberty interests with the investigative needs of intelligence agencies. Although Congress generally succeeded in striking an appropriate balance between these interests, the PlRA amendments effectively strip the courts of their power to provide any meaningful review when considering the modification or removal of nondisclosure orders. The level of deference that Congress apparently expects the courts to grant to the executive in matters of national security represents a low point in modern intelligence oversight, especially at [a] time when the ever expanding surveillance power of the executive requires even more vigilance from the courts and Congress.
The deployment of the mosaic theory to justify such deference can be seen as yet another example of the Bush administration's advocacy of the ‘unitary executive’ and its desire to insulate executive actions from congressional and judicial review. Such a move by the executive branch would unravel hard-won privacy and civil liberty protections that have proven so necessary in the conduct of intelligence investigations and leave those persons against whom NSL powers are used with no effective recourse when those powers are abused. The Church Committee [US Senate Select Committee to Study Governmental Operations with Respect to Intelligence Activities (1975)] concluded that if Americans confronted their mistakes and resolved not to repeat them, they would remain a people worthy of the best of their past. In the case of national security letter powers and authorities, and what amounts to an unchecked restriction of free speech, it would appear that the current administration is rushing to prove itself unworthy of such distinction. [excerpt]
Michael J. Greenlee, National Security Letters and Intelligence Oversight, in US National Security, Intelligence and Democracy 184, 204 (Russell A. Miller ed., 2008).