Over the next few weeks, a series of court filings are due that may shed substantial light on what Mueller has learned from people who once sat in Trump's inner circle.
That could happen as soon as Tuesday, when Mueller is scheduled to file a detailed memo in support of the sentencing of former National Security Adviser Michael Flynn. That memo would include information about any "bad acts" Flynn committed for which he was not charged, and details about his cooperation with the special counsel.
It's possible that filing will be sealed, which means the public won't see it until later. But on Friday, another filing is expected that legal experts say probably will not be sealed — a detailed explanation of why Mueller's office is withdrawing a plea agreement with former Trump campaign chairman Paul Manafort, including the "crimes and lies" Mueller alleges Manafort committed while he purported to be cooperating with the special counsel.
And then, on Dec. 12, former Trump lawyer Michael Cohen is expected to be sentenced in federal court in New York, in a hearing during which his other "bad acts," and his cooperation with Mueller, are likely to be further detailed.
"If these submissions are not filed under seal, I would expect to learn much more about the special counsel's investigation into the election of 2016 campaign than we know to date," said former federal prosecutor Daniel Goldman, an NBC News analyst.
Trump continued to appear to be distracted — and infuriated — by the Mueller investigation. In a series of tweets Monday, the president called for prison time for Cohen and appeared to praise his former associate Roger Stone, in a move that many legal experts said shattered presidential norms and raised the specter of witness tampering.
Stone "will not be forced by a rogue and out of control prosecutor to make up lies and stories about 'President Trump,'" Trump tweeted. "Nice to know that some people still have 'guts!'"View this graphic on nbcnews.com
Trump added in another tweet: "Bob Mueller (who is a much different man than people think) and his out of control band of Angry Democrats, don't want the truth, they only want lies. The truth is very bad for their mission!"
Attorney George Conway, the husband of Trump adviser Kellyanne Conway, replied to Trump on Twitter with a link to the federal statute on witness tampering, which prohibits any effort to "influence, intimidate, or impede," a witness in a criminal proceeding.
Trump may have reason to be concerned, given that in a late-night court filing in Manhattan Friday, Cohen's lawyers revealed that their client, a former Trump fixer, has been cooperating with four separate law enforcement groups: Mueller, the U.S. Attorney's Office in the Southern District of New York, the New York attorney general's office, and the New York State Department of Taxation and Finance.View this graphic on nbcnews.com
Cohen's attorney Guy Petrillo said in the filing that his client should get more credit for coming forward despite withering denunciations of the Mueller investigation by the president.
"In the context of this raw, full-bore attack by the most powerful person in the United States, Michael, formerly a confidante and adviser to Mr. Trump, resolved to cooperate, and voluntarily took the first steps toward doing so even before he was charged in this District," Petrillo wrote.
He added that Cohen "could have fought the government and continued to hold to the party line, positioning himself perhaps for a pardon or clemency, but, instead — for himself, his family, and his country — he took personal responsibility for his own wrongdoing and contributed, and is prepared to continue to contribute, to an investigation that he views as thoroughly legitimate and vital."
Cohen and his attorneys also cited the payments he made to women who allegedly had affairs with Trump, strongly implying in their filing that President Trump is the person referred to as "Client-1"— which had widely been assumed.
Petrillo wrote, "We respectfully request that the Court consider that as personal counsel to Client-1, Michael felt obligated to assist Client-1, on Client-1's instruction, to attempt to prevent Woman-1 and Woman-2 from disseminating narratives that would adversely affect the Campaign and cause personal embarrassment to Client-1 and his family."
The filing included 37 letters from friends and family of Cohen to Judge William Pauley, imploring the court for a reduced sentence or a sentence with no jail time.
One of the letters was from Cohen’s father, Maurice Cohen, an 83-year-old surgeon and Holocaust survivor.
He wrote, "So please where Michael is, let me be with him, and where he goes let me go. He is the oxygen in the air that I breathe."
Trump, in a highly unusual intervention by a president into a pending criminal case, tweeted Monday that Cohen "lied for this outcome and should, in my opinion, serve a full and complete sentence."View this graphic on nbcnews.com
Mueller's investigation is still progressing, despite the elevation to acting attorney general of Matthew Whitaker, who has been openly critical of the probe.
MSNBC anchor Nicolle Wallace reported last week that Whitaker had not assumed day-to-day supervision of the Mueller probe, leaving that task to Deputy Attorney General Rod Rosenstein. Justice Department spokeswoman Kerri Kupec did not dispute that but said that nothing had changed since the DOJ released a statement saying that Whitaker is in charge of all Justice Department matters.
If Mueller is allowed to proceed unimpeded, the public may learn a lot more about what he has uncovered in the coming weeks. Some legal experts believe he will use the court filings to inform the public about the progress of his investigation into whether the Trump campaign conspired with the 2016 Russian election interference operation.
"My best sense is there will be a lot of details" in the Manafort filing," former federal prosecutor Peter Zeidenberg told NBC News. "He's sort of depositing a few different important chapters in a few different courts where they would be in the reach of either Whitaker or anyone in Congress" to suppress it.
Former federal prosecutor Harry Littman, an NBC News contributor, said the Manafort filing promises to "give chapter and verse to really explain his real detail how he was lying."
Whether that reveals a lot or a little about the Mueller investigation, he said, depends on what Manafort is alleged to have lied about. For his part, Manafort denies lying.
The submission by Cohen's lawyers made it apparent that Cohen has no plans to waffle, as Manafort allegedly did — he is all-in on cooperating with the government. He apparently believes it's his only chance to get a break on sentencing for his crimes, and get on with his life.