See the Berger and Katz Cases.
http://caselaw.lp.findlaw.com/data/constitution/amendment04/05.html"Berger held unconstitutional on its face a state eavesdropping statute under which judges were authorized to issue warrants permitting police officers to trespass on private premises to install listening devices. The warrants were to be issued upon a showing of ''reasonable ground to believe that evidence of crime may be thus obtained, and particularly describing the person or persons whose communications, conversations or discussions are to be overheard or recorded.'' For the five-Justice majority, Justice Clark discerned several constitutional defects in the law. ''First, . . . eavesdropping is authorized without requiring belief that any particular offense has been or is being committed; nor that the 'property' sought, the conversations, be particularly described."
And in Katz:
"Just as Berger had confirmed that one rationale of the Olmstead decision, the inapplicability of ''seizure'' to conversations, was no longer valid, Katz disposed of the other rationale. In the latter case, officers had affixed a listening device to the outside wall of a telephone booth regularly used by Katz and activated it each time he entered; since there had been no physical trespass into the booth, the lower courts held the Fourth Amendment not relevant. The Court disagreed, saying that ''once it is recognized that the Fourth Amendment protects peo ple--and not simply 'areas'--against unreasonable searches and seizures, it becomes clear that the reach of that Amendment cannot turn upon the presence or absence of a physical intrusion into any given enclosure.'' 145 Because the surveillance of Katz's telephone calls had not been authorized by a magistrate, it was invalid; however, the Court thought that ''it is clear that this surveillance was so narrowly circumscribed that a duly authorized magistrate, properly notified of the need for such investigation, specifically informed of the basis on which it was to proceed, and clearly apprised of the precise intrusion it would entail, could constitutionally have authorized, with appropriate safeguards, the very limited search and seizure that the Government asserts in fact took place.''"
Katz gets to the heart of the matter - the only defect in the surveillence was the lack of a warrant.
Your freeper friend might be confused about the civil liability issue - if the AG can be sued, for example, for authorizing a warrantless search. That is a more complicated issue:
http://www.law.cornell.edu/anncon/html/art2frag42_user.htmlFinally, the 1978 FISA act specifically prohibits warrantless surveillence of "U.S. persons" (any legal resident of the United States). Domestic warrantless searches are a direct violation of existing law.