Everybody knew. Everybody of consequence at the Federal Bureau of Investigation and Justice Department understood fully in the middle of 2016—as the FBI embarked on its counterintelligence probe of Donald Trump—that it was doing so based on disinformation provided by Hillary Clinton’s campaign. That’s the big revelation from the transcript of the testimony Justice Department official Bruce Ohr gave Congress in August. The transcripts haven’t been released, but parts were confirmed for me by congressional sources.

Mr. Ohr testified...