Hillary Clinton will never “face the dock,” as lawyers are prone to say. But Harold T. Martin III will. On Thursday, when federal prosecutors announced charges against Martin under the Espionage Act for mishandling classified documents, people wondered, “but what about Hillary Clinton?” Fair question. In principle, both did the same thing. Martin, as a National Security Agency contractor, stored classified documents in his home, which was unauthorized. Clinton, as Secretary of State, stored classified documents on her personal server in her home. Again, unauthorized. On its face, it seems pretty much the same. Legally, the big difference is this:...