Apparently no espionage tool that Congress gives the National Security Agency is big enough or intrusive enough to satisfy the agency’s inexhaustible appetite for delving into the communications of Americans. Time and again, the N.S.A. has pushed past the limits that lawmakers thought they had imposed to prevent it from invading basic privacy, as guaranteed by the Constitution.

It was bad enough in 2008 when Congress allowed the agency to spy without a warrant on e-mails and text messages between Americans and foreign targets of an investigation. That already strained the Fourth Amendment’s protections against illegal searches, but lawmakers decided it was justified as part of a terror investigation.

It turns out, as Charlie Savage revealed in The Times on Thursday, that the N.S.A. went far beyond those boundaries. Instead, it copies virtually all overseas messages that Americans send or receive, then scans them to see if they contain any references to people or subjects the agency thinks might have a link to terrorists.

That could very well include innocent communications between family members expressing fears of a terror attack. Or messages between an editor and a reporter who is covering international security issues. Or the privileged conversation between a lawyer and a client who is being investigated.