This little-known Mueller report is required to be given to Congress — and will likely be 'fast-tracked' for the public

A little-known Justice Department regulation requires that a supplemental report be presented alongside special counsel Robert Mueller's findings — and the attorney general will have to give it to Congress.

Politico reported Wednesday that Attorney General William Barr will have to submit a report on all the times DOJ supervisors told Mueller "no" during the course of his investigation.

"No matter what the memo says, it’s expected to be one of the few items on a fast track for being made public that will be closely scrutinized for insights into the inner workings of the special counsel’s tight-lipped investigation," the report noted.

Though he's operated largely with independence, the special counsel has been subject to supervision by a number of Trump-appointed DOJ officials beginning with Deputy Attorney General Rod Rosenstein, then former acting AG Matt Whitaker and now Barr.

As Politico noted, the supplemental report could be blank — which could validate President Donald Trump's claim that he and the Justice Department did not interfere in Mueller's investigation.

If it does include information about denied requests, however, it could "open a road map for Democratic lawmakers who have already begun their own investigations into Russian interference in the 2016 elections, as well as the president’s conduct since taking office."

Sol Wisenberg, a former deputy who worked on Ken Starr's probe into former President Bill Clinton, told Politico that regardless of what the denial report contains, it will be "important."

“Assuming Mueller doesn’t indict anybody else, Trump will be able to say this guy wasn’t kept at all from going anywhere he wanted to go. So I think that’s a big deal," Wisenberg said. “On the other hand, if he was kept from going somewhere, that’s a big deal too. The Democrats will make a big deal about that. I think it’s important either way.”