Manafort was wiretapped for an investigation starting in 2014.  Well before the Trump campaign.   The FBI DID not bring a case and the tap stopped. Another investigation started in fall 2016.  After he left the Trump campaign. If Trump kept working with him after receiving Intel reports that Manafort was no good, what does that tell you?  Why was Trump still working someone he knew was taking millions of dollars in secret payments from oligarchs? Credibility?  Do you mean experience?  Manafort does not and did not have credibility at that point.