This is the story of the FBI's biggest con yet on the FISA Court. Newly declassified FBI documents (see pdf below) reveal the main source for the Steele Dossier and the FISA Warrants was a.suspected Russian Spy, someone who was on the FBI's radar for more than 10 years. Did the FBI tell the FISA Court? No.
The FBI's whole case against Carter Page and Team Trump was based on the Steele Dossier. Christopher Steele, who assembled the dossier, had no first hand knowledge of any of the information in it. He relied on a researcher he hired. Steele never corroborated anything in the dossier. But the FBI and the Department of Justice used it anyway as the justification for getting a FISA warrant on Carter Page.
The FBI and the Justice Department told the FISA Court that the information was verified, true and correct. It wasn't. While the FISA surveillance on Carter Page and Team Trump began in late October 2016, the FBI tried to verify the information in the dossier. It asked Christopher Steele who his primary source was. But Steele refused to divulge his name.
According to recently declassified FBI documents (see pdf below), the FBI figured out who the source was in December 2016. When the FBI checked its databases, they discovered that the source was, in fact, a suspected Russian spy that the FBI had on its radar screen more than 10 years earlier. The fact that the whole case rested on the word of a suspected Russian spy demolished the government's case. It should have closed the case and stopped the spying. It didn't.
When the government discovers information that goes against its theory of the case, it's required to tell the FISA Court. The FBI didn't. Instead it kept it a secret and obtained three more FISA search warrants to spy on Carter Page and Team Trump.
Senator Lindsey Graham, chairman of the Senate Judiciary Committee which conducts Congressional oversight of the FBI, declared that the case of the suspected Russian spy was the FBI's biggest fraud yet upon the FISA Court.