We should keep in mind that EVERYONE investigating Trump so far is a Republican, including Comey and Mueller. Congress is supposed to have oversight on the Executive Branch, but we all know how that has gone for the last two years. Now it's the Democrats' turn to investigate. That might just turn out a little different.
I don't see how Barr can do anything about that. For example, Mueller is now a non-employee of the Justice Department. They can subpoena him and ask in an open investigation on C-Span about anything. So Barr's and the Congress' efforts to hide the truth will all come to naught. It's pretty stupid, like you cat pulling the rug over the pile he missed getting in the litter box. It's almost like they want to get caught.