It doesn’t help that the Insider Threat Program has been adopted in agencies that have little or nothing to do with national security, including the Social Security Administration, the National Oceanic and Atmospheric Administration, the Department of Education and the Peace Corps. A tutorial for Agriculture Department employees includes a long list of “examples of behaviors that may indicate an individual has vulnerabilities that are of security concern.” These include sleeping at your desk — that might be a sign of alcoholism — and “expression of bizarre thoughts, perceptions, or expectations.” The list was imported, word for word, from a Defense Department document.

Other conspiracy theories involve groups that seem different: Suspected plotters can be identified by where they live, their racial or ethnic identity, or their social status. The enemy within,by contrast, can live anywhere and look like anyone. The men and women allegedly atop the cabal might be based in another country, but their puppets are ordinary neighbors, co-workers, members of your family. Anyone could conceivably be — or become — part of the plot.

This isn’t the first time an effort intended to protect national security has spiraled into something bigger, messier and more dangerous for individual liberty.