There is a subtle connection between the unfolding NSA metadata controversy and the controversy that has long plagued the administration's position on drone strikes, involving the impact of transparency on the legitimacy of the underlying legal architecture.
Transparency and the substantive legal foundations for controversial programs
First, consider the extent to which the substantive legal foundations for these programs are (or at least were) classified. In both the metadata and drone settings, the administration predicates the legality of its actions on statutory authority (the AUMF for drones, the FISA third-party records provision for metadata pre-collection). So far so good from a transparency viewpoint; statutes are of course known to the public. But in critical respects, both programs also require some important and non-obvious elements of statutory interpretation in order to get from the text to the particular elements of these programs that seem to cause the most controversy. The point is very clear with the metadata program, which depends on a non-obvious interpretation of the "relevant to an investigation" standard. And for drone strikes? The administration has been quite public in explaining its view that the AUMF authorizes them, including through an interpretation of the AUMF that extends beyond al Qaeda as such to reach al Qaeda's associated forces (at least when such groups engage in hostilities against the United States). But the administration has resisted public disclosure of which groups come within the scope of that understanding in its view, and has not made clear what factors suffice to make a group an associated force in this sense (nor, for that matter, has it been particularly forthcoming on these issues with Congress--in apparent contrast to the inter-branch transparency that may have occurred with the metadata program).
To be clear, I'm not suggesting that either interpretation is inappropriate. Nor am I suggesting that they involve comparable degrees of, well, creativity. I am simply pointing out that if a program depends on a classified and non-obvious interpretation of what the law permits, it is more likely to generate legal criticism if and when the details of the program leak. All other things being equal, this is an argument for bringing such interpretations into the light in advance, and entrenching them in statute if at all possible.
Procedural safeguards and transparency
Next, consider the extent to which the legitimacy of both the metadata program and the drone program also depend on the rigor of the procedural safeguards involved in their operation, and the impact on that dynamic of transparency. To be sure, we have heard a fair amount about the process involved in vetting nominations to kill lists, in recent years, but (i) the details are particularly patchy vis-a-vis the CIA and (ii) all of it depends on executive discretion in any event. As for the metadata program, we are beginning to hear details suggesting a very high-degree of rigor (particularly when it comes to accessing the resulting database in order to conduct target-specific queries), but though this appears likely to stem from a FISC mandate of some kind the fact remains that it is not an express part of a statutory architecture. Once more, all things being equal these programs would be far more legitimate and sustainable if these elements were brought into the light and entrenched in statute.