Judiciary Chairman Jerrold Nadler and Intelligence Chairman Adam Schiff, both Democrats, said that Mueller, who issued his report in April, would appear in an open session. They added that Mueller had agreed to the appearance under subpoenas.

The session, sure to be televised live, sets up one of the most dramatic hearings of the Trump presidency — and a confrontation between Democrats who have been pursuing investigations of the president since they took control of the House and Trump’s Republican supporters who dismissed the inquiries as fishing expeditions.

Until now, the White House has stymied investigations by Nadler, Schiff and other House Democratic chairmen by refusing to let present and former officials appear.

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Mueller said in his report that he couldn’t conclude whether Trump’s 2016 campaign conspired with Russia and also couldn’t exonerate the president from attempting to obstruct the investigation.

President Trump has repeatedly denounced the inquiry and steadfastly denied any wrongdoing. The president has tweeted in the past that “after total exoneration by Robert Mueller & the Mueller Report,” Democrats “want a Do Over.”

Soon after the Mueller hearing was announced, Trump simply tweeted: “Presidential Harassment!”

Donald J. Trump
@realDonaldTrump
Presidential Harassment!
Sent via Twitter for iPhone.

View original tweet.

Lawmakers from both parties are likely to tread carefully in their questioning of Mueller, a former F.B.I director, federal prosecutor and decorated Vietnam War veteran with a reputation for scrupulousness. He has said next to nothing about his investigation beyond the report, and made it clear that he’d prefer to say no more.

“Americans have demanded to hear directly from the special counsel so they can understand what he and his team examined, uncovered, and determined about Russia’s attack on our democracy, the Trump campaign’s acceptance and use of that help, and President Trump and his associates’ obstruction of the investigation into that attack,” Schiff and Nadler said in a statement.

In a letter accompanying the subpoenas, the chairmen tell Mueller that they understood that there were “certain sensitivities” associated with his testifying in public, including criminal investigations, some of which are continuing. That may indicate that they weren’t ruling out closed-door questioning on some matters.

“You have also explained that you prefer for the Special Counsel’s Office’s written work to speak for itself,” they added. “Nevertheless, the American public deserves to hear directly from you about your investigation and conclusions,” they write, saying they will work with Mueller to address his legitimate concerns.

The announcement comes after Republicans have taunted Nadler for not producing Mueller for a public hearing sooner.

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But next month’s hearing carries risks for both parties.

Some Democrats have taken comments by Mueller as a virtual invitation to open impeachment proceedings, a course that House Speaker Nancy Pelosi has resisted so far and has said could result in a political backlash because the Republican-controlled Senate would be unlikely to follow up by removing Trump from office.

Mueller has said Justice Department rules prohibit the indictment of the nation’s chief executive, and “the Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing.”

Now, Mueller will be available to directly answer whether impeachment proceedings are what he’s suggesting. If he says that, it will be difficult for Pelosi to continue putting off demands to move forward.

For Republicans, their gamesmanship in heckling Democrats for not subpoenaing Mueller to this point could come home to roost. Their claims that Democrats have misinterpreted Mueller’s findings could be proven false.

At a Judiciary hearing in April, after the release of the Mueller report, the top Republican on the Judiciary Committee, Doug Collins of Georgia, chastised Nadler and Democrats for not having produced Mueller as a witness.

Collins said that absent an impeachment inquiry, calling Mueller himself to testify would be the best way to learn about his findings — and that the hearing should be held.