Robert S. Mueller III discusses the investigation into Russian interference in the 2016 presidential election at the Justice Department on May 29, 2019. (Mandel Ngan/AFP/Getty Images)

Robert S. Mueller III will head to Capitol Hill next month reluctantly, knowing he will be thrust instantly into the teeth of a partisan storm.

Democrats will press the former special counsel to tell them more about President Trump’s wrongdoing than was already detailed in his 448-page investigative report, while settling for a televised spectacle that presents Mueller’s findings to new swaths of voters.

Republicans will try to cast their political opponents as intent on impeaching the president and unwilling to let go of an investigation that ended months ago without charges against Trump, while some are likely attack Mueller for his team’s perceived missteps.

On Wednesday, not 24 hours after it was revealed that Mueller would testify publicly pursuant to a subpoena from the House Judiciary and Intelligence committees, Trump lashed out at the man who investigated him. He accused Mueller of a crime, alleging without evidence that the special counsel had deleted text messages of two anti-Trump FBI employees who worked on the case. As he has in the past, Trump deemed Mueller’s work a “hoax.”

“The Mueller thing never stops,” Trump said before leaving the White House for a trip to Japan. “There was no collusion. There was no obstruction. There was no nothing.”

The president’s comments foreshadowed what are expected to be rancorous hearings July 17 at which Mueller — whose team interviewed nearly 500 people during the investigation — will become a witness himself, providing testimony that could shape the rest of the Trump presidency or the 2020 election.

“I think it will have a profound impact,” said House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.). “Just if he says what was in the report and says it to the American people so they hear it, that would be very, very important.”

A lawyer listed for Mueller on the subpoena did not respond to phone and email messages seeking comment. Senior members of Mueller’s former investigative team did not return messages either.

The appearance will be bifurcated, lawmakers said, with Mueller first testifying before Nadler’s committee, then moving to a second room for testimony before the Intelligence Committee. In total, Mueller is expected to speak publicly for about four hours.

Rep. Zoe Lofgren (D-Calif.), who sits on the Judiciary Committee, said the first portion would have a two-hour limit and hoped all members of the sizable committee would be able to ask questions.

Rep. Adam B. Schiff (D-Calif.), who leads the Intelligence Committee, said he had agreed that each of his panel’s members would be allowed five minutes for questions — which would take about two hours.

The Intelligence Committee is expected to follow its public hearing with a closed-door session with members of Mueller’s former staff, and Nadler said his panel might similarly meet with team members later.

Mueller has signaled that he would prefer not to testify, saying at a news conference last month, “I hope and expect this to be the only time that I will speak to you in this manner.” If forced to appear, he said, he “would not go beyond our report.”

Lawmakers will press him to do so anyway — hopeful they might unearth something new but eager merely to have the public hear Mueller speak in an extended appearance.

“As I’ve said a thousand times, having the Mueller report, even redacted, is like having the sheet music without ever having heard the song. And we’re going to hear the song when he comes and testifies,” said Rep. Denny Heck (D-Wash.), a member of the Intelligence Committee.

Mueller has said his team found insufficient evidence to allege a conspiracy between the Trump campaign and Russia to influence the election. But on the question of whether Trump obstructed justice, Mueller punted. His report said that because of Justice Department policy preventing the indictment of a sitting president, he would not decide — even privately — whether the evidence was sufficient to charge Trump with a crime.

Rep. Ted Deutch (D-Fla.), a member of the Judiciary Committee, said he wants to hear about why Mueller did not press Trump to testify. Mueller’s team wrote in its report that prosecutors never forced the issue with a subpoena because that would have caused a “substantial delay” and that investigators already had a “significant body of evidence” to explain the president’s actions.

“What’s missing from the Mueller report is any insight from the president of the United States about obstruction of justice, because he refused to speak directly with the team and he refused to answer any questions about obstruction of justice,” Deutch said.

Mueller, who served as FBI director from 2001 to 2013, is no stranger to congressional testimony. He testified dozens of times during his years leading the bureau, addressing such topics as the 9/11 terrorist attacks, the Boston Marathon bombing, NSA surveillance programs and other controversies of the day.

Those who know and have worked with Mueller say he always prepared meticulously.

“When I worked for him, he would prepare carefully for congressional testimony, even relatively simple testimony,” said Chuck Rosenberg, a former U.S. attorney and counsel to Mueller. “There would be briefers lined up, and they would come into his conference room one group after the other, to help him prepare for issues that might arise.”

Rosenberg said he expected Mueller would “stick to the script — to the report,” and that he could decline to answer particular questions.

“I don’t see him breaking much new ground or the hearings being all that interesting, except perhaps for the unfortunate political theater of it,” he said.

Privately, some House Democrats expressed fear that Mueller would not live up to the hype. Lawmakers felt they had an obligation to force him into the witness chair but said they worried that if he did not meet expectations, they might look inept and lose momentum toward impeachment proceedings.

“This can backfire. Big time,” one senior Democratic aide said, speaking on the condition of anonymity.

A senior Democratic leadership official said: “It’s kind of like, ‘Be careful what you wish for.’ We all kept saying we wanted to get Mueller. . . . We’re hoping it’s not a dud.”

Some of Trump’s staunchest Republican allies, meanwhile, signaled that they were willing to question the special counsel aggressively. Rep. Mark Meadows (R-N.C.) said soon after the hearings were scheduled: “Mr. Mueller better be prepared. I mean, there’s a lot more questions that Republicans have than Democrats.”

Lawmakers will, however, be without one critical tool. An inspector general’s report examining aspects of the investigation that Mueller took over, which Attorney General William P. Barr had said could come in May or June, is not expected to be released before Mueller’s testimony, people familiar with the matter said. The report might have criticized the FBI’s work, and given lawmakers material with which to question Mueller.

Rep. Jim Jordan (R-Ohio) on Wednesday wondered whether Mueller sought to hold off releasing his findings to influence the 2018 midterm elections.

“How much longer did it take Bob Mueller to figured that out? And did he potentially wait until after the 2018 midterms or what?” Jordan asked.

Jordan also said he and his GOP colleagues are planning to grill Mueller about his handling of FBI lawyer Lisa Page and FBI agent Peter Strzok, who worked on the case and were found by a previous inspector general’s investigation to have exchanged numerous anti-Trump text messages.

“Did he really check into how biased Mr. Strzok was and how that impacted his work?” Jordan asked.

Rep. Douglas A. Collins (Ga.), the Judiciary Committee’s top Republican, predicted that Mueller’s appearance would have no impact — “none” — on public opinion and noted that Mueller’s report had been out for two months.

“We brought a cavalcade of circus stars, and nothing’s changed,” Collins said, referring to former Nixon White House counsel John Dean’s recent testimony before the committee, an appearance that Republicans mocked repeatedly as being irrelevant to Mueller’s report.

“There’s no collusion, no conspiracy, no obstruction. The report has spoken for itself. . . . The problem is Democrats can’t get over . . . that they lost in 2016, so that’s why we’re going through this,” Collins said.

Trump renewed his attack on Page and Strzok on Wednesday, claiming during a wide-ranging interview with Fox Business Network that Mueller had “terminated” their texts.

“They’re gone,” Trump said. “And that’s illegal. That’s a crime.”

Trump seemed to be referring to a report made public in December that said the Justice Department inspector general could not recover texts from the phones assigned to Strzok and Page for their work with Mueller because by the time investigators requested the devices, they had been reset in preparation for others to use them.

The inspector general wrote there was “no evidence” that Strzok and Page “attempted to circumvent” the FBI’s data-retention policies, and the “content of the text messages did not appear to be a factor” in whether and how the messages were retained. The report makes no mention of Mueller’s playing any role in the deletion of texts and notes that the Justice Department had told investigators it “routinely resets mobile devices to factory settings” when they are returned to be given to other users.

Strzok was removed from Mueller’s team in July 2017 — and ultimately fired from the FBI last year — after the communications were discovered. Page separately left the team and later the bureau.

Trump also on Wednesday alleged again that the FBI had “spied on my campaign” and referred to its use of opposition research funded by Hillary Clinton’s campaign to help advance its investigation. He accused Democrats of wanting a “do-over.”

“My only response to Mueller is, ‘Does it ever stop?’ ” Trump said. “ ‘After all of these years and times and people, does it ever stop?’ ”

It is likely that Republican lawmakers might take up some of those attacks, hoping to rattle the former special counsel. Rosenberg, who worked with Mueller when Mueller was FBI director, said he had seen lawmakers make similar efforts in the past.

“I’ve seen them try,” he said. “I’ve never seen them succeed.”

Karoun Demirjian contributed to this report.