From the very same OIG report he's using as validation of his claim:
https://www.justice.gov/storage/120919-examination.pdf
"C. Absence of FBI CHSs Inside the Trump Campaign
All of the witnesses we interviewed told the OIG that the FBI did not try to recruit members of the Trump campaign as CHSs, did not send CHSs to collect information in Trump campaign headquarters or Trump campaign spaces, and did not ask CHSs to join the Trump campaign or otherwise attend campaign related events as part of the investigation.
Using the methodology described above, we found no information indicating otherwise."
McCarthy is either an idiot who didn't bother to read the report, or a lying sack of wet garbage that is deliberately misleading his constituents, whom he knows full well will never read it. I'm betting the latter.
Conservatives,
this is fake news;
this is a hoax.