But the big question is how much of what the special counsel concludes – after an investigation repeatedly blasted as a "hoax" and a "witch hunt" by the President – will be made public or even sent to Congress.  Whenever it is filed, Mueller's report will mark a critical point in the Trump presidency, given the gravity of the accusations against his team, and offer theoretical possibilities of conclusive answers about the last White House race.
The reclusive former FBI director's findings could also put the United States on the road to a new and divisive impeachment saga, if he finds collusion with Russia and an attempt by the President to obstruct justice to cover it up.
If there is no case for Trump to answer, Mueller could at least partially lift a cloud that has haunted the White House every day of his presidency, though a flurry of spin-off cases meant the President's legal exposure is far from over.
It will be a fraught political ti me, since so many Americans have invested so much emotion in the outcome, whether they are liberals who dream of Trump being ousted from power or supporters who buy his claims of a huge "hoax."
Yet key players in Washington and many Americans beyond, transfixed by the barely believable drama leading up to the final report, at least at first, may be down.
Mueller's endgame is obscured because no one really knows exactly what he will report and the information that Barr will choose ̵
The uncertainty is almost certain to spark a new struggle between Congress, the White House and the Justice Department that could lead to litigation and has every chance of reaching all the way up to the Supreme Court.
Mueller's filing could also herald the reclusive prosecutor's own exit from the stage – likely after not speaking to the American people from the beg inning to the end of his investigation.
That old fashioned reticence, as well as a stellar career in law enforcement, is one reason why Mueller's conclusions will carry such weight – whether his report is ultimately critical of the President or leaves him in the clear.
What does Mueller know – and what will he say?
The special counsel has run one of the most impenetrable Washington investigations in memory. He has, however, sprinkled clues throughout a growing library of indictments and court memos.
While he has yet to openly accuse anyone in Trump's orbit of colluding with the Russians, Mueller has laid out 10 criminal cases, seen four people sentenced to prison, secured one conviction and trial, extracted seven guilty pleas and charged 37 people and entities with crimes.
CNN's Katelyn Polantz contributed to this report.