People have a reasonable expectation of privacy in their private digital communications such as email, and therefore the Fourth Amendment protects those communications. It‘s a simple extension of the Supreme Court’s seminal 1967 ruling in Katz v. United States that the Fourth Amendment protected a telephone conversation held in a closed phone booth. But in a brief recently filed in a criminal terrorism case arising from surveillance of a United States citizen, the government needs only a few sentences to argue this basic protection doesn’t apply, with potentially dramatic consequences for the rest of us.