The FBI made 17 significant errors and omissions in its investigation of Team Trump. That's the finding of the Inspector General for the Department of Justice. This episode focuses on the biggest blunder of all.
The FBI's biggest blunder in the case involved its accusation that there was probable cause to believe that Carter Page, a foreign policy advisor for the Trump campaign, was actually a Russian agent. The fact is that Page worked for the CIA, not the Russians. And the CIA told the FBI that Carter Page was a source for the agency. That vital fact was never presented to the FISA Court. But it was the single most important fact the undercut the government's claim that Page was the agent of a foreign power.
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.