The FBI and Department of Justice used unconfirmed, uncorroborated 3rd, 4th and 5th hand information as the legal basis to spy on the Trump campaign.
The FBI and Department of Justice relied on Christopher Steele's dossier of dirt on the Trump campaign to get a FISA warrant to spy on the campaign. But the critical information in the dossier was never corroborated in any way by Steele, his sources, the FBI or the Department of Justice. The dossier was multiple levels of hearsay yet it was used to obtain multiple search warrants from the Foreign Intelligence Surveillance Court.
Investigators for the House Intelligence Committee spent months trying to figure out who paid for the Steele dossier. The document was a political dirty trick. So, the transaction was designed to be hard to trace. In the end, it took a court case to get to the truth. Here's what was revealed:
√ See link below to Washington Post story published October 24, 2017
One of the most important resources to understanding "Spygate" is a report by the Department of Justice Inspector General. It was issued in December, 2019. SpyGate Truth repeatedly refers to it, citing page numbers for the source information we report. You can look for yourself. Here's a link to the full report. Be advised, however, it's 474 pages long and does not read like a spy novel.