Thirty-five years ago in United States v. Choate, the courts ruled that the Postal Service may record “mail cover,” i.e., what's written on the outside of an envelope — the addresses of sender and receiver.
The National Security Agency's recording of U.S. phone data does basically that with the telephone. It records who is calling whom — the outside of the envelope, as it were. The content of the conversation, however, is like the letter inside the envelope. It may not be opened without a court order.
The constitutional basis for this is simple: The Fourth Amendment protects against “unreasonable searches and seizures,” and there is no reasonable expectation of privacy for what's written on an envelope. It's dropped in a public mailbox, read by workers at the collection center and read once again by the letter carrier. It's already openly been shared, much as your phone records are shared with, recorded by, and mailed (or emailed) back to you by a third party, namely the phone company.
Indeed, in 1979 the Supreme Court (Smith v. Maryland) made the point directly regarding the telephone: The expectation of privacy applies to the content of a call, not its record. There is therefore nothing constitutionally offensive about the newly revealed NSA data-mining program that seeks to identify terrorist networks through telephone-log pattern recognition.
But doesn't the other NSA program — the spooky-sounding James Bond-evoking PRISM — give you the willies? Well, what we know thus far is that PRISM is designed to read the emails of non-U.S. citizens outside the United States. If an al-Qaida operative in Yemen is emailing a potential recruit, it would be folly
As former Attorney General Michael Mukasey explains, the Constitution is not a treaty with the rest of the world; it's an instrument for the protection of the American citizenry. And reading other people's mail is something countries do to protect themselves. It's called spying.