The way to find out is for the FBI to release the contents of its investigation. One might hope that the FBI would have a transcript of its July 2 interview of Mrs. Clinton. But in his testimony to Congress the following week, Mr. Comey admitted that the agency neither put her under oath nor had a stenographer present.

FBI agents involved in such interviews customarily prepare a list of questions. One agent poses them, while the remaining agents take notes that are used to draft a “Report of Interview,” commonly called by its document number, “the 302.”

To prove that she told Americans in public the same things she told the FBI in private, as she claims, Mrs. Clinton should ask Mr. Comey to release the agency’s list of prepared questions and the 302 from her interview. Only then might voters have the information to decide for themselves whether Mrs. Clinton is being truthful or layering one lie on another.

These documents would also help resolve another question: What advice did Mrs. Clinton receive regarding her home-brew email server? “I relied on and had every reason to rely on the judgments of the professionals with whom I worked,” she said on Fox News. “In retrospect, maybe some people are saying, well, among those 300 people, they made the wrong call.” So did she tell the FBI who these unnamed professionals were and what they advised on the server? Or is this only another deception?