Of all the tall tales James Comey has told, none compare to the line he fed President Trump at their infamous January 2017 dinner. As recounted in the former Federal Bureau of Investigation director’s memo about that evening, “I said I don’t do sneaky things, I don’t leak, I don’t do weasel moves.”

The Justice Department’s inspector general begs to differ. In a new report about Mr. Comey’s handling of those memos, Michael Horowitz demonstrates that Mr. Comey in 2017 was consistently leaky and sneaky. The report refutes any...