The FBI also waited until November to talk to anyone who had worked with Mr. Steele during his tenure at Britain’s MI6—after the FBI had fired him for talking to the press. Only then did it learn that former colleagues believed Mr. Steele was prone to “rash judgments” and had a “lack of self awareness.” It didn’t bother talking to his primary source until January 2017, when it discovered that much of the reporting Mr. Steele provided was gossip.

The IG confirms that the FBI also made no effort to “determine who was financing Steele’s election related research.” Mr. Steele told the IG he knew who his paymasters were by late July, and Justice official Bruce Ohr told Congress that he warned FBI officials in August that Mr. Steele was hired by somebody “related to the Clinton campaign.” A team of FBI officials interviewed Mr. Steele in early October. Nobody asked about his employer.

Nor did they ask if Mr. Steele had been the source of a Sept. 23, 2016 Yahoo News article that revealed the FBI was looking into Trump-Russia collusion. Various case agents at the time of publication expressed alarm that Mr. Steele was talking to the press (he was), and a draft version of the FISA application fingered him as the leaker. But the IG says nobody at the October meeting asked Mr. Steele if he talked to the press. The final FISA application incorrectly asserted to the court that Mr. Steele had not.