According to a half dozen current and former U.S. intelligence officials who know the real story:
The CIA decision to alert the FBI in September 2016 that there was intelligence showing the Russians believed Hillary Clinton was "stirring up" a false collusion narrative to "vilify" Donald Trump was sent as a red flare, one of several warnings that the bureau had embarked on a fool's errand that could become a source of acute institutional embarrassment.
Likewise, America's premier spy agency also warned America's premier law enforcement agency it was focused on the wrong guy in Trump adviser Carter Page. CIA told FBI that Page was a U.S. intelligence asset, not a Russian stooge. The FBI hid that crucial information from the FISA Court, in one instance even falsifying a document.
Evidence now made public shows at least 10 separate Clinton allies fed collusion allegations to the FBI in 2016 and early 2017, an avalanche of political pressure aimed at getting agents to investigate Trump during the campaign and after his election win.