With debate about NSA spying continuing in the Senate, it's worth looking at some of the historical and modern precedents for protecting our communications and communications data. A few highlights:

• The earliest precedent for protection of communications in the United States is the treatment of mail. The founders used postal mail to communicate their revolutionary ideas and even to plan their insurrection against the tyranny of King George, so they prioritized protecting the privacy of the mail. In the Act of Feb. 20, 1792, passed a few short years after ratification of the Constitution, the U.S. Congress enshrined protections for mail in the law, creating heavy fines for opening or delaying mail.

• The Supreme Court confirmed the existence of constitutional protection for postal communications in Ex Parte Jackson. In that 1877 case, the Court described the Fourth Amendment's guarantees in very interesting and clear language: "Letters and sealed packages ... are as fully guarded from examination and inspection, except as to their outward form and weight, as if they were retained by the parties forwarding them in their own domiciles." Though we place mail in the hands of government agents, the Fourth Amendment protects it like it's inside our homes.

• The year Ex Parte Jackson case was decided, both Western Union and the Bell Company began providing voice telephone service. The Supreme Court addressed constitutional protection for phone calls some decades later in 1928. The Olmstead case was wrongly decided, we now know. It found that telephone communications weren't protected by the Constitution. So the dissents are where to look for precedential language. Justice Brandeis's famous dissent spoke of the "right to be let alone," but Justice Butler provided thinking and language that should have more lasting value: "The contracts between telephone companies and users contemplate the private use of the facilities employed in the service," he wrote. "The communications belong to the parties between whom they pass." The communications belong to the parties. That's a fasacinating and important way to think about our communications, as property that we own.

When the Court reversed Olmstead in 1967's Katz decision, it unfortunately and inadvertently produced a Fourth Amendment doctrine basing constitutional protection on "reasonable expectations of privacy." People do reasonably expect privacy in their communications, but "reasonable expectations" doctrine is not well equipped for administering the Fourth Amendment. We saw that in Smith v. Maryland, the 1979 case in which the Court used no research or even consideration of the opposing view in finding that people have no expectation of privacy in data about their phone calls. Happily, the Court has eschewed "reasonable expectation" doctrine in many recent cases.

When the Second Circuit Court of Appeals ruled that the NSA spying program is illegal a few weeks ago, it treated data as property. When we reduce our thoughts and records to digital form and send them over the Internet, we're doing the same thing the founders did when they wrote letters and put them in the mail. Those communications are still ours, and they should be protected in transit as if they are in the home. America's private telecommunications system is not like the U.S. mail, of course. We're not handing our calls over to the government like we hand our letters to the U.S. Postal Service. Our calls and Internet communications should be more protected than the mail because we are using service providers that are obligated by contract and regulation to protect our privacy.

The communications data the NSA is accessing belongs to the parties between whom it passes. It is not the government's to take---not without a particularized warrant based on the requisite level of suspicion. There's good precedent for that.