The FBI as an organization knew for sure in early 2017, likely earlier, that Trump was not a Russian spy. But the bureau allowed the process to drift on through the Mueller report and all the rest. Mueller established a “dossier validation” unit that found none of Christopher Steele’s reporting could be corroborated. Mueller also shut down attempts by FBI agents to investigate a Clinton crony with high-level connections to Putin, and failed to complete an espionage investigation into Steele’s Russian primary sub-source.
Imagine how different Trump's term would have been had we all known with certainty what the FBI did. No Maddow, no walls closing in, no insinuations America's president was dealing cards to the Russians right out of the Oval Office. What was lost for the nation’s business we'll never know.