When former special counsel Robert Mueller testifies before Congress on July 17, he can expect a slew of questions from both Democrats and Republicans about the details of his 22-month long Russia probe.

Democrats are likely to focus on the obstruction portion of the investigation, in hopes that they can mount a case for the impeachment of President Donald Trump. Republicans will likely key in on Mueller’s finding that the Trump campaign did not conspire with the Russian government to influence the 2016 election.

Save for a brief statement on May 29, Mueller has said nothing publicly about how his investigation unfolded. And though he produced a 448-page report of the investigation, numerous questions remain about how prosecutors developed their cases and arrived at their conclusions about Trump and the campaign.

Here is a list of 27 questions that lawmakers in both parties can ask Mueller.

When did you determine that there was no conspiracy between the Trump campaign and Russia?

Some congressional Republicans have asserted that Mueller figured out early on in his investigation — which started on May 17, 2017 — that there was no conspiracy or collusion between the Trump campaign and Russian government.

Mueller’s report said that prosecutors were unable to establish that the campaign conspired with Russia, but the report did not go into detail about when that conclusion was reached.

What areas of investigation were authorized in former Deputy Attorney General Rod Rosenstein’s Aug. 2, 2017 scope memo? Why did Rosenstein wait more than two months to lay out the scope of the investigation?

Rosenstein’s memo explained the May 17, 2017 appointment order for the special counsel, and gave greater detail about what areas Mueller should investigate.

According to Mueller’s report, the memo explained that Mueller could investigate whether former Trump campaign advisers Carter Page, Paul Manafort and George Papadopoulos broke the law “by colluding with Russian officials.” It also explained that Mueller was authorized to investigate Manafort’s consulting work in Ukraine, whether Papadopoulos was a foreign agent of Israel, and four separate sets of allegations about former national security adviser Michael Flynn.

Critics of the investigation have questioned the timing of the scope memo, which Rosenstein submitted several days after the FBI raided Manafort’s home and after Papadopoulos was arrested.

Did President Trump obstruct the FBI or special counsel’s investigation?

Mueller’s team investigated 10 separate incidents for potential obstruction of justice by Trump. The report details the president’s orders to White House officials to find a way to remove Mueller as special counsel.

But Trump and his lawyers have noted that Mueller was never removed from the investigation. Rosenstein, who oversaw the probe, was also not fired. Trump’s lawyers have noted that he provided more than 1.4 million documents to investigators and instructed White House officials to provide voluntary interviews to the special counsel’s team.

Would you have charged President Trump with a crime if not for the Justice Department policy against indicting sitting presidents?

Mueller’s hearings are likely to focus heavily on this question.

It is still unclear whether Mueller declined charging Trump with obstruction because of a longstanding DOJ policy against indicting sitting presidents. Mueller can clear up whether he would have indicted Trump if it wasn’t for that policy.

What was the official reason for removing Peter Strzok from the special counsel’s team? Did his text messages indicate bias against Trump? 

Strzok, who served as deputy chief of the FBI’s counterintelligence division, was removed from Mueller’s team in late July 2017 after the discovery of anti-Trump text messages he exchanged with FBI lawyer Lisa Page. He was reportedly canned after a brief meeting with Mueller. Strzok, who opened the investigation of the Trump campaign, has testified to Congress that Mueller did not give a specific reason for the decision to remove him from the special counsel’s team. He has also denied that his disdain for Trump did not affect how he conducted the investigation.

How important was the Steele dossier to the overall investigation?

The FBI relied on the dossier, which was authored by former British spy Christopher Steele, to obtain four Foreign intelligence Surveillance Act (FISA) warrants against former Trump campaign aide Carter Page. The FBI also investigated the allegations in the dossier that the Kremlin was blackmailing Donald Trump and that the campaign was involved in a “well-developed conspiracy of co-operation” with Russia to influence the election.

Mueller’s report all but debunked several key allegations in the dossier. That poses a potential problem for investigators if the probe relied heavily on Steele’s reporting.

Did the FBI mislead the FISA court in applying for warrants against Carter Page? 

Republicans have accused the FBI of misleading the FISA court by relying on Steele’s unverified dossier in applications for spy warrants on Page. Steele alleged that Page met in Moscow in July 2016 with two Kremlin insiders to discuss ways to influence the 2016 election.

Page has vehemently denied meeting with either Kremlin insider. And despite being under surveillance for a year, he was not charged in the special counsel’s probe. The investigation was unable to establish a conspiracy involving Page or anyone else on the Trump team. And though the FBI asserted in its FISA applications that Page may have been a Russian agent, the Mueller report said that prosecutors were unable to establish that any Trump associates worked as agents of Russia.

The FBI’s FISA applications were also scant on details about who hired Steele. The Clinton campaign and DNC are not identified in the applications.

When did investigators figure out that the Steele dossier’s claim that Michael Cohen visited Russia was inaccurate?

The special counsel’s report poured cold water on one of the dossier’s most significant collusion allegations: that Cohen, a former Trump lawyer, visited Prague in August 2016 to meet with Russians to discuss paying off hackers. The allegation was often cited by Trump critics as evidence of a massive conspiracy between the campaign and Kremlin.

But Mueller’s report seemingly accepted Cohen’s claim that he has never visited Prague. It has still not been revealed when investigators figured out that the allegation was false, and why they did not publicly rebut the allegation.

Who was interviewed in connection with the dossier, and why is the dossier mentioned only a few times in the report? 

Steele was interviewed twice by the special counsel’s office, reportedly in September 2017. But it is unclear whether Fusion GPS, the firm that hired Steele, had any contact with investigators.

The dossier is barely mentioned in the Mueller report — only 14 times. Some Republicans have criticized Mueller for not going deeper into the origins of the dossier, or explaining how it factored into the investigation.

What other allegations in the dossier were debunked by the investigation? What is the theory for why Steele published false information?

The Mueller report all but debunked the dossier’s core allegation, which was that the Trump campaign was involved in a “well-developed conspiracy of co-operation” with the Russian government. Steele, who was working for the DNC and Clinton campaign, also alleged that the Kremlin had blackmail material on Trump.

The apparent inaccuracies in the dossier have drawn concern from former intelligence community professionals, as well as Attorney General William Barr.

He testified to the Senate Judiciary Committee on May 1 that he is “concerned” that the dossier was disinformation planted with Steele by Russians.

Did investigators reach a conclusion on the so-called “pee tape” mentioned in the dossier?

The report has one mention of an alleged tape of Trump, but does not settle the question of whether investigators came to a conclusion about whether a tape actually exists.

In Steele’s first memo of the dossier, dated June 20, 2016, he alleges that sources said that the Kremlin had a blackmail tape of Trump with prostitutes at a Moscow hotel room in 2013. The dossier claims that Trump looked on as the prostitutes urinated on each other.

Trump has vehemently denied the claim, and Michael Cohen told the House Intelligence Committee on Feb. 28 that he does not believe the tape exists.

Mueller’s report refers to a text message conversation between Cohen and a friend, Giorgi Rtskhiladze. In the Oct. 31, 2016 text, Rtskihiladze said that he “stopped the flow of some tapes” from Russia. Rtskhiladze has since said that he had heard a rumor from someone in Russia about tapes, but did not believe that they existed.

Were you able to speak with any of Steele’s sources? 

Mueller’s report says that investigators were unable to meet with Sergei Millian, a businessman who is reported to be one of Steele’s main sources. Millian declined several offers by the special counsel to meet, according to the report.

Millian, who had contact during the campaign with Papadopoulos, is reported to be one of the sources behind the allegation about the Moscow blackmail tape.

It is not known whether Steele revealed the identities of other sources, or whether any of them met with the special counsel’s team.

Steele may have identified some of his sources during a meeting with a State Department official on Oct. 11, 2016. Notes from that meeting refer to former Russian foreign intelligence chief Vyacheslav Trubnikov and Putin aide Vladislav Surkov as “sources” for Steele.

Steele also shared a list of his sources with David Kramer, a longtime John McCain associate and former State Department official who provided the dossier to BuzzFeed News.

Do you have any problems with Barr’s review of the surveillance activities against the Trump campaign and the origins of the Russia probe?

Barr tapped U.S. Attorney John Durham to conduct a comprehensive review of the U.S. government’s activities against the Trump campaign. Durham is reportedly looking at how the FBI, CIA and U.S. intelligence community gathered intelligence on Russian efforts to meddle in the election.

Was Crossfire Hurricane properly predicated?

Mueller’s report says that the FBI opened its investigation — dubbed Crossfire Hurricane — on July 31, 2016 after the bureau received a tip from a foreign government regarding George Papadopoulos. The source has previously been identified as Alexander Downer, a former Australian diplomat who met Papadopoulos in London on May 10, 2016.

Downer said that Papadopoulos told him that Russia might have information on Hillary Clinton. After WikiLeaks released stolen DNC emails on July 22, 2016, Downer and the Aussies decided to pass their tip on to the FBI.

From there, Peter Strzok opened a counterintelligence file on the Trump campaign.

The initial suspicion about Papadopoulos appears to have flamed out. He pleaded guilty in the special counsel’s probe to lying to the FBI, but he was not charged with conspiracy. He was also not accused of taking part in any activities related to Democrats’ emails.

Former FBI officials have defended the decision to open the investigation based on the Papadopoulos tip.

Why was George Papadopoulos arrested so early in the investigation? 

Papadopoulos was arrested at Washington-Dulles International Airport on July 27, 2017, making him the first known arrest connected to the special counsel’s probe.

Papadopoulos has said he believes that he was arrested early in the investigation in order to keep him quiet about his contacts with Stefan Halper, a former Cambridge professor who is reported to be a longtime FBI informant.

Halper contacted Papadopoulos in September 2016, and offered the young Trump aide $3,000 and a trip to London to discuss writing an academic paper. Papadopoulos accepted the offer and met with Halper, as well as Azra Turk, a government investigator who posed as Halper’s assistant.

Why was Papadopoulos investigated as a possible foreign agent of Israel?

One surprising revelation in the report was that Papadopoulos was investigated as a possible foreign agent of Israel. Papadopoulos worked as an energy consultant and on energy issues at various think tanks. Before the release of Mueller’s report, Papadopoulos had claimed that prosecutors threatened to charge him as an Israeli agent.

What is the evidence that Joseph Mifsud and Konstantin Kilimnik are Russian assets?

The Mueller report portrays Mifsud, a Maltese professor who met with Papadopoulos, and Kilimnik, a Ukrainian business partner of Manafort’s, as Russian agents. But Mifsud has also worked closely with Western intelligence agencies and has visited the State Department.

Kilimnik, who has been accused of having ties to Russia’s GRU, was a source for the State Department.

Why was Mifsud not charged with making false statements to the FBI when the special counsel’s report says that he lied about the specifics of his contacts with Papadopoulos?

Both Mifsud and Papadopoulos were accused of making false statements to the FBI about their interactions with each other during the 2016 campaign. Yet of the two, only Papadopoulos faced charges related to the false statements. He pleaded guilty on Oct. 5, 2017 to lying to the FBI about the extent of his contacts with Mifsud.

Mifsud was not charged in the investigation, even though Mueller’s report says that Mifsud lied in a February 2017 interview about the details of his interactions with Papadopoulos.

What were the four sets of allegations about Michael Flynn that were investigated?

The report says that Flynn was investigated for four sets of allegations. The retired lieutenant general pleaded guilty on Dec. 1, 2017 to lying to the FBI about his conversations with Russian ambassador Sergey Kislyak during the presidential transition period. He was also investigated for his lobbying activities on behalf of the Turkish government before the 2016 election.

But Flynn was seemingly under investigation before he began the lobbying work, and prior to his contacts with Kislyak. It has still not been explained why else Flynn would have been under investigation. One possibility is his trip to Moscow in December 2015 to a gala hosted by RT, the Russian media company.

Did the special counsel’s team rely on Stefan Halper or any other confidential informants?

Halper had contact with three Trump campaign aides: Papadopoulos, Carter Page, and Sam Clovis. He stayed in touch with Page the longest — through September 2017. It is unclear whether Halper provided information directly to the special counsel or if he continued working through the FBI.

Halper may also have had a role in gathering intelligence on Flynn. Halper was part of a group that hosted Flynn at Cambridge in February 2014, when Flynn served as director of the Defense Intelligence Agency. Halper reportedly expressed concerns to American and British intelligence about Flynn’s interactions at the Cambridge event with Svetlana Lokhova, a Cambridge researcher.

Lokhova sued Halper on May 24, accusing him of planting false allegations about her and Flynn in the press.

The report says that prosecutors were unable to establish that the campaign conspired with Russia. Did investigators find any evidence of a conspiracy? If so, why did it not lead to charges?

The report is somewhat vague about how much evidence, if any, was found of a conspiracy between the Trump team and Russia. In its legalistic tone, the report says that “the investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities.”

That leaves open the possibility that Mueller & Co. did find evidence of a conspiracy, but that the evidence was not strong enough to support a federal case. Mueller could answer how close prosecutors came to filing conspiracy charges.

What counterintelligence concerns were found during the investigation? Did investigators find any evidence that Russia blackmailed Trump or any of his associates, or that Russia had compromising information on Trump & Co.?

Mueller’s report said that an FBI team remained in close contact with the special counsel regarding the counterintelligence portion of the investigation. As Democrats have pointed out, the Mueller report does not delve into whether Russia has leverage over Trump or any of his associates.

House Intelligence Committee Chairman Adam Schiff has refocused his efforts on whether Russia had leverage over Trump through potential business deals.

Would impeachment proceedings against Trump be warranted?

Any endorsement by Mueller for impeachment of Trump would be a game-changer. The party is divided over whether to begin impeachment proceedings, with Speaker Nancy Pelosi decidedly against the idea.

How was the report compiled? Which prosecutors contributed the most to the report?

Few details have surfaced about the nuts and bolts of how the report was put together. Some Republicans have speculated that Andrew Weissmann, an aggressive prosecutor known as Mueller’s “pit bull,” played a significant role in compiling the report.

What exactly did the special counsel’s office object to in the BuzzFeed article that alleged that President Trump instructed Michael Cohen to lie to Congress?

In a rare move, the special counsel knocked down a BuzzFeed story published on Jan. 17 that alleged that President Trump directed Michael Cohen to lie to Congress about the extent of his negotiations to build a Trump Tower in Moscow.

A spokesman for the special counsel said that the story was inaccurate, but did not explain exactly what parts of the story were at issue.

Mueller’s report said that Cohen told prosecutors that he and Trump “did not explicitly discuss whether Cohen’s testimony about the Trump Tower Moscow project would be or was false, and the President did not direct him to provide false testimony. Cohen also said he did not tell the President about the specifics of his planned testimony.”

Despite the rebuke of BuzzFeed’s report, the outlet continues to maintain that its initial story is broadly accurate.

Did the special counsel have to investigate any leaks from inside the office? 

Mueller’s team was widely praised as running a leak-proof operation, but Trump supporters disputed that characterization throughout the investigation.

Did any inaccurate news stories harm the investigation, and why didn’t the special counsel’s office publicly rebut more of them?

Besides the BuzzFeed article, numerous other news stories published during the special counsel’s probe proved to be false. McClatchy reported in two articles that the special counsel had evidence placing Michael Cohen in Prague during the campaign, as the dossier claimed.

CNN published several inaccurate stories about key areas of interest in the special counsel’s probe.

On Dec. 8, 2017, the network falsely reported that Donald Trump Jr. received an email on Sept. 4, 2016 with a link to unpublished WikiLeaks documents. It turned out that Trump Jr. actually received the email 10 days later, after the WikiLeaks documents had been released.

CNN also reported on July 27, 2018, that Michael Cohen planned to testify that Trump Jr. told his father beforehand about a June 9, 2016 meeting at Trump Tower with a group of Russians.

Both Trumps had denied that the president was aware of the meeting before it occurred. Cohen would later testify that he believed that Trump Jr. may have told his father about the meeting, but that he had no direct evidence to back up his speculation.

Mueller could also be asked why his office remained silent in the face of many of the false reports.

A spokesman for Mueller did issue a vague warning about McClatchy’s reports about Cohen visiting Prague, but that was more than a year after the dossier was published. Failing to correct the story and others left the impression that the campaign did conspire with Russia.