U.S. Attorney General nominee William Barr has been confirmed by the senate.  The vote was 54-45 with three democrats voting to support Barr: Kyrsten Sinema (AZ), Doug Jones (AL) and Joe Manchin (WV); with one republican, senator Rand Paul (KY), voting against the nomination.
Now that he is confirmed Barr is officially supervising the special counsel probe of Robert Mueller.  It is also likely that after a transition period Deputy AG Rod Rosenstein will depart.
One of Barr’s responsibilities will be to determine what, if anything, to tell congress about the Mueller probe once it is completed.  Perhaps the best way to think about the Mueller report is to think about your local police department (detective or DA) doing an investigation on a subject and completing that task.

At the conclusion of the inquiry, perhaps using a grand jury, if there is no determination of criminal wrongdoing – the investigator does not outline the investigation in a report to the general public.
The basic premise behind this standard process is simple.  Everyone is innocent unless they can be proven to be guilty.
If everyone who was ever investigated had the internal investigative material made public it would be profoundly unfair to the target.  It would be even more unfair if the investigator was allowed to frame a public report, with their own internal biases and innuendo, in lieu of their ability to find criminal wrongdoing.
Now amplify that simple fairness issue x 1,000 and consider how severely political federal investigators might produce such a document against their opposition.  It is easy to see how such a report can be weaponized for political benefit.  The weaponization and benefit is the goal of the current Democrat leadership.
However, specifically to address these issues, and in an attempt to remove the political weaponization possible within the special counsel statute, the DOJ framed the ending of a special counsel investigation such that a summary of investigative finding is delivered to the U.S. Attorney General, who then puts out a public statement (of sorts) describing the conclusion (the finding).

(WaPo) […] The special-counsel regulations call for Mueller to provide the attorney general with a “confidential report” explaining who he did and did not decide to prosecute, and for Barr to notify Congress of the investigation’s end and of any steps Mueller wanted to take that were vetoed.
The regulations give Barr some latitude to release information publicly, though Barr noted at his confirmation hearing that under normal circumstances, prosecutors would not reveal information about those they choose not to charge. (more)

Pelosi, Schumer and the Democrats do not want William Barr to be able to write a summary, a public statement, based on the report delivered to him by Robert Mueller.
Instead, the Democrats want the report from Mueller, including all the investigative trails that were exhausted, so they can exploit aspects of the inquiry that were not able to be proven.  That allows them to weaponize “innuendo” and “possibility” for political benefit.