Over at Balkinization, Marty Lederman looks at the current dispute over the scope of NSA wiretapping powers and offers the following take:

[I]t must be the case that the NSA's aim is not simply to surveil foreigners who it already suspects as being part of Al Qaeda. It can obtain a FISA order as to those folks. What it wants, instead, is to be able to intercept foreign communications coming over domestic wires where (i) it does not have probable cause to believe that any of the parties is a terrorist or agent of a foreign power; and (ii) there is a chance that some of the intercepted communications will be with persons in the U.S.

FISA does not allow surveillance where both of those conditions obtain. (Indeed, insofar as the surveillance picks up U.S. persons in such cases, without proof that either party is the agent of a foreign power, it would probably violate the Fourth Amendment, too, at least according to the pre-FISA cases that considered the question.)

  As to the first point, I think that is clearly right. Federal law plainly allows the government to monitor foreign people with no connection to U.S. soil so long as the monitoring occurs outside the United States. Such persons have no Fourth Amendment rights under Verdugo-Urquidez, and FISA does not apply. So the government wants to do the same monitoring from the U.S. switches that they can do from monitoring posts outside the U.S. That is, they want to take out the relevance of where the monitoring site happens to be. The question is whether FISA allows particular measures to try to do that given the possibility of picking up calls and e-mails to the U.S.

  Second, there are two notable reasons to think that the Fourth Amendment is not implicated in this setting. First, there are some precedents indicating that if you call someone whose calls are being monitored without violating their reasonable expectation of privacy, then it does not violate your Fourth Amendment rights to have the call recorded. See, e.g., United States v. McNulty, 47 F.3d 100, 104-106 (4th Cir. 1995) (person speaking to a person on a cordless call being monitored by the police). I don't think the Supreme Court has addressed this theory, and I gather some VC readers will find it unpersuasive, but there are such cases on the books.

  Second, the Fourth Amendment generally is only triggered by intentional conduct. See Brower v. Inyo County, 489 U.S. 593 (1989) ("Violation of the Fourth Amendment requires an intentional acquisition of physical control."). If the government collects a call and doesn't know that it is conducting a search or seizure under the Fourth Amendment -- because it doesn't know a party has Fourth Amendment rights -- it may be that under Inyo there is no Fourth Amendment violation. (This latter argument is subject to the uncertainty as to whether wiretapping is a search or seizure or both, as well as how the mens rea requirement applies to searches, but I think it is still worth noting.)