Mueller carried out an investigation. Barr is limiting and controlling access to Mueller's report in ways that are partisan. He's a Trump appointee, sitting on a report that could lead to Trump's impeachment. He's between a rock and a hard place.
Until that report is fully released and objectively interpreted (not by him), he's going to be the center of attention. Once the report is fully vetted and explained to the public, attention switches back to Donald.