Important to note that the FBI offered money for this dossier which many have called into question. The dossier was put together as opposition research commissioned by a Hillary ally. So basically they were using fake/unreliable opposition research for their ‘probable cause’ in their application for the warrant.
Washington (CNN)The FBI last year used a dossier of allegations of Russian ties to Donald Trump’s campaign as part of the justification to win approval to secretly monitor a Trump associate, according to US officials briefed on the investigation.
The dossier has also been cited by FBI Director James Comey in some of his briefings to members of Congress in recent weeks, as one of the sources of information the bureau has used to bolster its investigation, according to US officials briefed on the probe.
This includes approval from the secret court that oversees the Foreign Intelligence Surveillance Act (FISA) to monitor the communications of Carter Page, two of the officials said. Last year, Page was identified by the Trump campaign as an adviser on national security.