F.B.I. Opened Inquiry Into Whether Trump Was Secretly Working on Behalf of Russia – The New York Times

 

In the months before the 2016 election, the F.B.I. was also already investigating four of Mr. Trump’s associates over their ties to Russia. The constellation of events disquieted F.B.I. officials who were simultaneously watching as Russia’s campaign unfolded to undermine the presidential election by exploiting existing divisions among Americans.

Source: F.B.I. Opened Inquiry Into Whether Trump Was Secretly Working on Behalf of Russia – The New York Times

This is the buried lead. At the time of his campaign, there were four people under investigation by the FBI for ties to Russia. This seems improbable unless there was collusion.