The Fix Is In, as they say.
Consider that Trump's DOJ has already briefed The White House (but not the Congress) on the Mueller Report and that this was done while Barr's team was busy redacting it. The report itself (or what's left of it) will only be released to the Congress after the press conference - thus denying any of the reporters who'd be asking questions any chance of reading it before hand.
And as you're considering all that you should be asking yourself this question: If the report is, in fact, a "total exoneration" of Trump, then why is any of Barr's framing necessary?
Don't you think that if it were a "total exoneration" of Trump, then they'd just simply open up the damn thing for everyone to read and go, "See?"
The Fix is in.