Soon, the dust will settle from special counsel Robert Mueller's report, and Americans will have a fuller understanding of why prosecutors concluded there wasn't evidence to establish that Donald Trump and Russia colluded to hijack the 2016 election.

At that point, many voters exhausted by the fizzling of a two-year scandal, once billed as the next Watergate, will want to move on like a foodie from an empty-calorie shake.

But a very important second phase of this drama is about to begin, as Attorney General William Barr, Department of Justice (DOJ) Inspector General Michael Horowitz and Senate Judiciary Committee Chairman Lindsey Graham (R-S.C.) put the Russia collusion investigators under investigation.

Their work will be, and must be, far more than just a political boomerang.

It must answer, in balanced terms, whether the FBI was warranted in using the most awesome powers in the U.S. intelligence arsenal to spy on Republican presidential nominee Donald Trump's campaign at the end of the 2016 election.

Investigators must determine, with neutrality, whether the bureau improperly colluded with paid agents of Democratic rival Hillary Clinton's campaign - Fusion GPS and its British operative, Christopher Steele - and then tried to hide those political ties and other evidence from the nation's secret intelligence court.

For the likes of FBI castoffs James Comey, Andrew McCabe and Peter Strzok, or Obama-era intelligence bosses John Brennan and James Clapper, there will be the additional uncomfortable reality that the Russia collusion narrative that they so publicly weaved through testimony, TV appearances, for-profit books and leaks, turned out to be as unsubstantiated as the Loch Ness monster.

The process of meting out accountability has begun.

Horowitz, my sources tell me, has interviewed between 50 and 100 witnesses in his exhaustive probe. Graham and his predecessor as Judiciary chairman, Sen. Chuck Grassley (R-Iowa), laid out the most important investigative issues they saw in a letter last year. This month, former House Intelligence Committee Chairman Devin Nunes (R-Calif.) sent a letter to DOJ identifying eight potential criminal referrals. His committee last year also released a memo on abuses of the Foreign Intelligence Surveillance Act (FISA) that may have occurred during the Russia probe.

And President Trump reportedly is readying an order to declassify five key buckets of documents on alleged FBI abuses.

My sources agree these 10 questions are the most important to be answered in the forthcoming probes:

1.) When did the FBI first learn that Steele's dossier was funded by the Clinton campaign and the Democratic Party and written by a partisan who, by his own admission, was desperate to defeat Trump? Documents and testimony I reviewed show senior DOJ official Bruce Ohr first told his colleagues about Steele's bias and connections to Clinton in late summer 2016. Likewise, sources tell me a string of FBI emails - some before the bureau secured its first surveillance warrant - raised concerns about Steele's motive, employer and credibility.

2.) How much evidence of innocence did the FBI possess against two of its early targets, Trump campaign advisers George Papadopoulos and Carter Page? My sources tell me that agents secured evidence of the innocence of both men from informants, intercepts and other techniques that was never disclosed to the Foreign Intelligence Surveillance Court judges in the case. I'm told learning exactly the sort of surveillance used on Page also may surprise some people.

3.) Why was the Steele dossier used as primary evidence in the FISA warrant against Page when it had not been corroborated? FBI testimony I reviewed shows agents had just begun checking out the dossier when its elements were used as supporting evidence, and that spreadsheets kept by the bureau during the verification process validated only small pieces of the dossier while concluding other parts were false or unprovable. And, of course, former FBI lawyer Lisa Page admitted that, after nine months of investigation, the dossier's core allegation of Trump-Russia collusion could not be substantiated.

4.) Why were Steele's biases and his ties to the Clinton campaign - as well as evidence of innocence and flaws in the FISA evidence - never disclosed to the FISA court, as required by law and court practice?

5.) Why did FBI and U.S. intelligence officials leak stories about evidence in the emerging Russia probe before they corroborated collusion, and were any of those leaks designed to "create" evidence that could be cited in the courts of law and public opinion to justify the continuation of a flawed investigation?

6.) Did Comey improperly handle classified information when he distributed memos of his private conversations with Trump to his lawyers and a friend and ordered a leak that he hoped would cause the appointment of a special counsel after his firing as FBI director?

7.) Did the CIA, FBI or Obama White House engage in activities - such as the activation of intelligence sources or electronic surveillance - before the opening of an official counterintelligence investigation against the Trump campaign on July 31, 2016?

8.) Did U.S. intelligence, the FBI or the Obama administration use or encourage friendly spy agencies in Great Britain, Australia, Ukraine, Italy or elsewhere to gather evidence on the Trump campaign, leak evidence, or get around U.S. restrictions on spying on Americans?

9.) Did the CIA or Obama intelligence apparatus try to lure or pressure the FBI into opening a Trump collusion probe or acknowledge its existence before the election? Text messages between alleged FBI lovebirds Strzok and Page raised concerns about "pressure" from the White House, the "Agency BS game," DOJ leaks and the need for an FBI "insurance policy." And, as Strzok texted at one point in August 2016, quoting a colleague: "The White House is running this."

10.) Did any FBI agents, intelligence officials or other key players in the probe provide false testimony to Congress? McCabe already has been singled out by the inspector general for lying about a media leak to an internal DOJ probe, and evidence emerged this year that calls into question Fusion GPS founder Glenn Simpson's testimony about his contacts with Ohr.

If Barr, Horowitz and Graham can answer these questions and release the still-secret evidence underlying their conclusions, Americans finally will have the wherewithal to answer the most troubling of all the questions raised about the Russia collusion narrative:

Was this a case of bureaucratic bungling, or an intentional effort to use the U.S. intelligence community for a political dirty trick aimed at defeating Trump at the polls and, later, delegitimizing his election?

It's a question we all should want to be answered.

John Solomon is an award-winning investigative journalist whose work over the years has exposed U.S. and FBI intelligence failures before the Sept. 11 attacks, federal scientists' misuse of foster children and veterans in drug experiments, and numerous cases of political corruption. He serves as an investigative columnist and executive vice president for video at The Hill.