The FBI went to bat for Hillary Clinton on Tuesday, saying that handling emails with classified information — even when it’s marked — isn’t enough to prove she had “knowledge or intent” to break the law. In a letter to congressional investigators, the FBI’s chief liaison to Capitol Hill said Mrs. Clinton did handle three messages with a “(C)” mark next to paragraphs, “ostensibly indicating” the following information as classified. But Jason V. Herring said that’s not enough to show she was negligent. Mr. Herring also questioned whether the laws against handling classified material in a “grossly negligent” way would...