Last week, two senators challenged even the accuracy of a fact sheet prepared by the N.S.A. to counter Mr. Snowden’s claims about the phone data and Internet collection programs. Agency officials did not defend themselves; the fact sheet simply disappeared, without explanation, from the agency’s Web site.
Newly disclosed slides from an N.S.A. PowerPoint presentation on the agency’s Prism database of Internet data, posted on Saturday by The Washington Post, reveal that the F.B.I. plays a role as middleman between the N.S.A. and Internet companies like Google and Yahoo. The arrangement provides the N.S.A. with a defense, however nominal, against claims that it spies on United States soil.