On Thursday morning, Attorney General William Barr will release special counsel Robert Mueller's report on Russian interference in the 2016 election, potential collusion, and obstruction of justice.

The report could have a sweeping impact on President Donald Trump's legacy. Hopefully, it will close a convoluted and arduous chapter in US history. Here are nine major questions:

Will we learn anything new on collusion?

The big question driving Mueller's two-year investigation was simple: Did anyone affiliated with Trump's presidential campaign coordinate with the Russians to help Trump win the election?

According to Barr, the answer was no. In a letter to lawmakers last month, he quoted from Mueller's original report: "[T]he investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities."

But it's still possible that Mueller's report reveals new nuggets about Trump-Russia contacts, and who in the campaign knew about these contacts. (Trump has said all along that he didn't know.) Many of these interactions are well-documented in the public domain, though there might be more to learn.

Did Mueller see "collusion" as a crime?

The legal community will be watching to see how Mueller went about investigating "collusion." Federal investigators search for violations of specific US laws. So, which laws came into play?

As Trump's lawyers loved to point out , there is no specific US law that says "collusion" is a crime. Instead, Mueller relied on other laws to indict two dozen Russians trolls and hackers. Many were charged with defrauding the US government by "impairing" and "obstructing" lawful government functions, like the ability of the Federal Election Commission to regulate elections.

It's unclear if Mueller used the same legal theory to investigate Americans for collusion. Perhaps more severe charges could have been on the table. (Prosecutors balked when a judge asked if they considered treason charges for Trump's former national security adviser Michael Flynn.)

What about obstruction of justice?

Barr said Mueller thoroughly examined whether Trump obstructed the investigation, but ultimately decided not to offer a conclusion one way or the other. Because Mueller left the topic "unresolved," Barr said he stepped in and decided that no charges were appropriate.

This was by far the most puzzling part of Barr's letter. Mueller's job was to be an independent arbiter who could make tough decisions like these. He was there to keep these decisions out of the hands of political appointees like Barr, who was Trump's pick to run the Justice Department.

In his summary, Barr hinted that Mueller's original report might feature elements of the internal debate on obstruction. He said Mueller described the dilemma as a series of "difficult issues."

It will be critical to see how Mueller explains his decision not to make a decision on obstruction. In the words of former FBI Director James Comey: "There must be some very good reason why Bob Mueller did it this way." We'll just have to wait a little longer to hopefully get that answer.

How did Mueller assess Trump's statements and tweets?

As part of the obstruction inquiry, prosecutors examined "a number of actions by the President," Barr said, and he specifically noted that most of those actions "took place in public view."

The report will probably include Mueller's assessment of how those public actions fit into a larger mosaic of obstruction. Trump's defenders have argued that he can't illegally undermine an investigation through public words and tweets. We'll find out soon if Mueller agrees.

Barr's carefully worded letter said the public already knows about "most," but not all, of the events that Mueller scrutinized as part of the obstruction inquiry. That means there are more shoes to drop, new episodes of potential wrongdoing that could be damaging to Trump.

Were Trump Jr. or Kushner investigated but never charged?

The regulations don't say much about what should go in Mueller's report. But they do say Mueller needs to explain "prosecution or declination decisions reached by the Special Counsel."

We already know all the "prosecution decisions." Mueller brought criminal charges against six Trump associates, 26 Russian nationals, three Russian companies, and two others.

But we don't know the "declination decisions." That is, the people Mueller investigated but decided not to charge. This section of the report could be highly redacted. But even if it's blacked-out, we could still get a glimpse into how long the list is. This could include other Trump associates or even members of Trump's family, like Donald Trump Jr. or his son-in-law Jared Kushner.

Will Mueller offer ethical or moral conclusions?

The investigation is over, and Mueller isn't bringing charges against anyone else. But that doesn't mean everyone whose conduct was scrutinized will walk away with a clean bill of health.

It's possible that the report concludes that some actions were not criminal but showed poor judgment or were highly unethical. What comes to mind is Trump Jr.'s eagerness to accept dirt on Democratic nominee Hillary Clinton from Russians at the Trump Tower meeting.

Mueller is known as a straight-shooter. He was hired to look for crimes, not to be the morality police. It seems unlikely that he would offer moral judgments like these, but it's possible.

This would be akin to "pulling a Comey," who in July 2016 offered a scathing critique of Clinton's behavior while simultaneously clearing her of criminality in the email investigation. Internal Justice Department guidelines tell prosecutors they shouldn't besmirch the reputations of uncharged individuals -- a point that Barr noted on during his confirmation hearing.

How many related investigations are ongoing?

During the course of his investigation, Mueller referred some cases to other prosecutors.

Some of investigations efforts have already produced results, like the indictment against Flynn's business partner in the Eastern District of Virginia for undisclosed foreign lobbying, or the charges against Cohen in the Southern District of New York for campaign finance violations.

But others are still underway, and some aren't even publicly known yet. Mueller likely included details about these investigation in his report. In a letter to lawmakers , Barr said he would redact "material that could affect other ongoing matters, including those that the Special Counsel has referred to other Department offices."

The length of the redactions could be telling, and it should be easy to identify which redactions are about ongoing probes. Barr said at a House hearing on Tuesday that all the redactions will be "color-coded" to identify why the material was blacked-out.

How did Mueller investigate the Russians?

The Mueller probe produced two major indictments against Russians for interfering in the 2016 election. These indictments featured exquisite details about the Russian operation to manipulate American voters using social media and to steal sensitive emails from prominent Democrats.

The CIA and NSA likely helped Mueller's team get these insider details, like the Google searches of alleged hackers and the monthly budget of the St. Petersburg-based troll farm.

Unfortunately, it's all but assured that large chunks of this part of the report will be blacked-out. US intelligence agencies get to scrub the report for "sources and methods," and will redact any information that they think could hurt national security or put human sources in danger if it became public.

Which countries assisted the investigation?

Mueller's team "made 13 requests to foreign governments for evidence," according to Barr's summary of their investigation. The report might identify which countries were involved. It could be included in the "tables and appendices" that Barr said come after the nearly 400-page report.

Any additional revelations of foreign governments cooperating with Mueller, even in an entirely routine way, could lead to diplomatic fallout. Trump has long viewed the probe was a "witch hunt" and he would likely turn his ire on any foreign leader whose country helped Mueller out.