The US justice department has demanded that Robert Mueller limit his congressional testimony to “the boundaries of [his] public report”, ahead of the former special counsel’s appearance before two House of Representatives’ committees.
Mr Mueller will appear at the highly anticipated hearings, in front of the judiciary and intelligence committees, on Wednesday.
Bradley Weinsheimer, the US assistant deputy attorney general, warned the 74-year-old that his testimony “must remain within the boundaries of your public report because matters within the scope of your investigation were covered by executive privilege.”
“These privileges would include discussion about investigative steps or decisions made during your investigation not otherwise described in the public version of your report,” Mr Weinsheimer added, in a letter sent to Mr Mueller.
The department’s letter comes just weeks after Mr Trump issued a similar warning on Twitter.
“Robert Mueller is being asked to testify yet again,” the president said earlier this month.
“He said he could only stick to the Report, & that is what he would and must do. After so much testimony & total transparency, this Witch Hunt must now end. No more Do Overs. No Collusion, No Obstruction.”
Democrats are expected to ask the former special counsel about Donald Trump’s alleged misconduct.
Mr Mueller’s public report, published in March 2019, discussed numerous examples of contact between Russian officials and Mr Trump’s campaign, but found no evidence of a criminal conspiracy.
The report also laid out examples of 10 incidents in which the US president sought to hinder the probe.
Despite his findings, Mr Mueller did not draw a conclusion on whether Donald Trump obstructed justice.
William Barr, the US attorney general and a member of the Trump administration, later ruled that there was not enough evidence to bring obstruction charges against the president.
Mr Barr’s ruling has proved highly controversial and has been called into question by Democrats.
Jerrold Nadler, the Democratic chair of the judiciary committee, said he thought there was “substantial evidence” that Mr Trump had committed “high crimes and misdemeanours”.
Several Democrats in the House of Representatives are pressing to impeach the president, but such evidence would be required for proceedings to begin.
The Democratic leadership has avoided an impeachment attempt, as Nancy Pelosi, the house speaker, believes it would harm the party’s 2020 electoral chances.
But the party remains split, with progressives such as Al Green continuing to call for the president’s removal.
Mr Mueller completed his investigation into Russian election interference in March 2019, following a probe which took nearly two years.
A spokesperson for Mr Mueller said no one at the justice department, the White House or congress would read the 74-year-old’s statement before he delivered it on Wednesday.
The former special counsel has been using offices at his former law firm WilmerHale and working with a small team to prepare for the back-to-back hearings.
Mr Mueller has previously said that he will not go beyond the content of the report in his congressional testimony.
“He will come well prepared,” the spokesperson added.
“His team has been working on this for a while and they will be ready for whatever comes their way.”