What explains the FBI's deep faith in Trump dossier author Christopher Steele?

The FBI placed so much faith in Steele because he was a former British spy — a fellow professional — who had worked with the bureau a few years earlier in the world soccer corruption investigation. The FBI specifically referenced Steele’s history in the Page application to the FISA court, known as FISC.

“The FBI stated to the FISC that ‘based on [Steele’s] previous reporting history with the FBI, whereby [Steele] provided reliable information to the FBI, the FBI believes [Steele’s] reporting to be credible,'” Grassley and Graham wrote, quoting from the surveillance application.

But there were two problems with Steele’s credibility, according to the referral. The first was the lack of corroborating evidence. The other was convincing evidence that Steele lied to the FBI.