FBI

When the FBI went to the FISA court to get permission to surveil Carter Page they were refused. Later they went back with the additional information in the Steel dossier and received the warrant. It was later discovered that the dossier contained un-varifyable information which made it unacceptable for a warrant. The dossier was the product of a Democratic operation from April 2016 to December 2016 and was focused on getting dirt on Trump. This sort of thing is common and called operational research. Christopher Steel, a former spy, was hired to prepare the dossier and thus the name. It contained allegations of misconduct, conspiracy and cooperation between Trump and the Russian government. The dossier's 17 reports allege that Trump campaign members and Russian operatives had conspired to cooperate in Russian election interference to benefit Trump. The US intelligence community took the allegations seriously and the FBI investigated every line of the dossier and identified and spoke with at least two of Steele's sources. The DNC and the Clinton campaign, working through their attorney Marc Elias. In April 2016, Elias hired Fusion GPS to perform research on Trump and they paid Fusion one million dollars. The FBI relied on the Steele debunked dossier inserting key parts from it into their application to the FISA court. Agents did this without telling the court that wording was taken directly from a political rumor sheet paid for by the Clinton campaign.