...Such messages contain sensitive “keywords” distinguishing them from unclassified information, even if the material didn’t bear a classified heading as she claims. The secretary would have known better, the department officials say, because she was trained to understand the difference when she was “read in” on procedures to ID and handle classified information by diplomatic-security officials in 2009. Clinton also went through a so-called “read-off” when she left office in 2013. In that debriefing, security officials reminded her of her duty to return all classified documents, including ones in which the classification status is “uncertain,” which would have included the...