Declassified footnotes to a Justice Department inspector general report show that the Federal Bureau of Investigation team investigating members of the Trump campaign received classified reports in 2017 identifying key pieces of the Steele dossier as products of a Russian disinformation campaign. This might be only the tip of the iceberg because other recently declassified information demonstrates that even more disinformation may have been planted in Christopher Steele’s reporting.

Let that sink in. The FBI knew that at least...