Several people now have pled or been convicted of crimes because they associated with Trump. Michael Cohen even pled guilty to a bundle of crimes that include non-crimes. If Flynn, Cohen, and Manafort had not associated with Donald Trump, no charges would ever have been brought against them.
We are not seeing a criminal conspiracy investigation going on, we are seeing the Impeach-Trump dossier being assembled. All criminal charges being leveled are actually political charges. In other words, the charges originate from a political strategy not from a specific alleged criminal act sparking an investigation.