Still, this leaves questions unanswered. How did those reviewing the emails define “personal”? For instance, if Mrs. Clinton had emailed a foreign government about a donation to the Clinton Foundation, was that message—whatever its interest to watchdogs or voters—tossed in the trash bin?

The law says that no one has to use email, but it is a crime (18 U.S.C. section 1519) to destroy even one message to prevent it from being subpoenaed. Prosecutors charging someone with obstruction don’t even have to establish that any investigation was pending or under way when the deletion took place. As T. Markus Funk explained in a journal article for the National Association of Criminal Defense Lawyers, the prosecutor “need only prove that the defendant shredded the documents, at least in part, to make life more difficult for future investigators, if and when they eventually appear.”

Legal commentators call this “anticipatory obstruction of justice,” and the law punishes it with up to 20 years imprisonment. The burden of proof is light. The Justice Department manual advises that section 1519 makes prosecution much easier because it covers “any matters” or “’in relation to or contemplation of’ any matters.” It adds, “No corrupt persuasion is required.”