The culture in Washington, particularly among senior-executive officials, is pervasively risk-averse, and has been for some time. When I took office as U.S. attorney general in 2007, members of my staff saw to it that I stopped carrying a BlackBerry, lest I inadvertently send confidential information over an insecure network or lest it be activated, without my knowledge, and my communications monitored.

When I attended my first briefing in a secure facility, and brought a pad to take notes, my chief of staff leaned over and wrote in bold capital letters at the top of the first page, “TS/SCI,” meaning Top Secret, Secure Compartmentalized Information—which is to say, information that may be looked at only in what is known as a SCIF, a Secure, Compartmentalized Information Facility. My office was considered a SCIF; my apartment was not.

The point he was making by doing that—and this is just the point that seems to have eluded the former secretary of state—is one of common sense: Once you assume a public office, your communications about anything having to do with your job are not your personal business or property. They are the public’s business and the public’s property, and are to be treated as no different from communications of like sensitivity.

That something so obvious could have eluded Mrs. Clinton raises questions about her suitability both for the office she held and for the office she seeks.