The Justice Department on Monday told former special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE that he should limit his Wednesday testimony before Congress to the four corners of his public report on Russian interference.

“Any testimony must remain within the boundaries of your public report because matters within the scope of your investigation were covered by executive privilege, including information protected by law enforcement, deliberative process, attorney work product, and presidential communications privileges,” Associate Deputy Attorney General Bradley Weinsheimer wrote in a letter to Mueller that was obtained by The Hill.

“These privileges would include discussion about investigative steps or decisions made during your investigation not otherwise described in the public version of your report,” Weinsheimer wrote.

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“Consistent with standard practice, Department witnesses should decline to address potentially privileged matters, thus affording the Department the full opportunity at a later date to consider particular questions and possible accommodations that may fulfill the committees’ legitimate need for information while protecting Executive Branch confidentiality interests,” he added.

It was already expected that Mueller was unlikely to speak beyond what is spelled out in the redacted version of his 448-page report on Russian interference into the 2016 election and possible obstruction of justice by President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE. The new letter all but guarantees that.

Weinsheimer noted that he was responding to a July 10 letter from Mueller that requested guidance from the department “concerning privilege or other legal bars applicable to potential testimony in connection” with the subpoenas issued by the House Judiciary and Intelligence committees for his appearance.

Weinsheimer reiterated statements made by Attorney General William Barr Bill BarrHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Bipartisan representatives demand answers on expired surveillance programs YouTube to battle mail-in voting misinformation with info panel on videos MORE that it is ultimately Mueller’s decision to testify. He emphasized that Mueller should not reveal anything related to the redacted portions of the report — which conceal grand jury material, details on ongoing investigations, classified material and information on third parties.

Mueller, who is now a private citizen after leaving his post as special counsel, is slated to testify in back-to-back hearings before the Judiciary and Intelligence panels on Wednesday, a combined appearance that is expected to last roughly five hours.

In his only public remarks on the investigation on May 29, Mueller indicated he did not want to testify before Congress. He also said any testimony would not go beyond his report, stating, “The report is my testimony.” Democrats eventually subpoenaed him to testify last month.

In a brief interview Monday evening, Mueller’s spokesman Jim Popkin told The Hill that the former special counsel would stick closely to the details of the report in his public appearance.

“As I think he made crystal clear then, you can expect him to stick as much as he can to the four walls of the Mueller report,” said Popkin, pointing to his May 29 statement.

Popkin said that Mueller would make an opening statement to Congress that would not be viewed by the Justice Department beforehand. He also said Mueller would make the public version of the report a statement for the congressional record.

Mueller has been preparing for his testimony with a small group of attorneys from the special counsel’s office using space provided by his former law offices of Wilmer Hale, Popkin said.

Democrats are hoping for Mueller to bring to life portions of his report that paint a damning picture of Trump’s efforts to thwart and gain control of the investigation.

Some have tempered expectations, saying they don’t expect the hearing to yield new information, but said nonetheless that the hearing will be successful if they’re able to shine a light on what the special counsel’s investigation found.

Mueller did not reach a conclusion one way or another on whether Trump obstructed the Russia investigation, saying that the Justice Department Office of Legal Counsel opinion prevented him from even considering the question. Mueller is unlikely to answer questions Wednesday about whether he would have charged Trump if not for that opinion.

Mueller’s report also details numerous contacts between the Trump campaign and Russia, however the investigation found insufficient evidence to charge associates of the campaign with conspiring with Moscow to meddle in the election. Trump and his allies have heralded that result as vindicating him of allegations of “collusion” with Russia.

Still, Mueller’s marathon appearance on Capitol Hill could generate bad headlines for the White House, attracting wall-to-wall media coverage and elevating some of the more unsavory details of his exhaustive report.