WASHINGTON — James B. Comey, the former F.B.I. director, will testify publicly about his role in the investigation into Russian meddling in the election and any possible connections to the campaign of President Trump, the Senate Intelligence Committee announced Friday.
Mr. Comey’s handling of the investigation, including his several conversations with Mr. Trump since his election, has taken on added importance since his dismissal and subsequent reports that the president had asked Mr. Comey to shut down part of the inquiry, and then later called him a “nut job” in meetings with Russian officials.
“I am hopeful that he will clarify for the American people recent events that have been broadly reported in the media,” said Senator Richard M. Burr, Republican of North Carolina and the chairman of the committee. Senator Mark Warner, Democrat of Virginia, said he expected Mr. Comey to “shed light on issues critical to this committee’s investigation of Russian interference in the 2016 election.”
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The announcement that Mr. Comey would testify followed closely the disclosure by the Justice Department that Rod J. Rosenstein, the deputy attorney general, had talked with Attorney General Jeff Sessions about replacing Mr. Comey last winter, before either man had been confirmed for his position in the Trump administration.
Mr. Rosenstein revealed that detail in two briefings to members of Congress this week, according to remarks released Friday by the Justice Department. His testimony provides fuller details about Mr. Trump’s termination of the top law enforcement official investigating whether his campaign colluded with the Russian government to influence the outcome of the 2016 election.
During his meetings with lawmakers, Mr. Rosenstein said that his conversations with Mr. Sessions revealed his long-held belief that Mr. Comey should be replaced based on his public statements related to the investigation of Hillary Clinton, beginning in July 2016.
“Among the concerns that I recall were to restore the credibility of the F.B.I., respect the established authority of the Department of Justice, limit public statements and eliminate leaks,” he said, echoing the sentiments he had outlined in a May 9 memo that the White House released publicly that day and cited as the basis for the firing.
But on May 8 — the day before Mr. Rosenstein drafted that three-page memo, he told lawmakers — he had learned of Mr. Trump’s intention to remove Mr. Comey from the job.
“I thought it was appropriate to seek a new leader,” he said, expressing more direct support for the firing than he had in his more measured memo, which stopped short of endorsing a particular action but rather outlined what he called Mr. Comey’s “serious mistakes” and noted that any possible decision to dismiss Mr. Comey “should not be taken lightly.”
Mr. Trump acknowledged, in an interview with NBC News, that he had decided to fire Mr. Comey before reading the memo by Mr. Rosenstein.
The release of the testimony followed what was otherwise an unremarkable appearance before House members on Friday, the day after he briefed senators, that left many lawmakers frustrated by Mr. Rosenstein’s refusal to answer questions about the investigation into Russian meddling in the election.
“What we did not get a clear understanding of was whether the memo was written with or without the urging of the White House,” Representative G. K. Butterfield, Democrat of North Carolina, said.
Representative Seth Moulton, Democrat of Massachusetts, said there was “considerable frustration” among lawmakers Friday as Mr. Rosenstein declined to answer more detailed questions about the events leading to the abrupt termination.
“This renewed my confidence that we should not have confidence in this administration,” Mr. Moulton said. Asked whether that included Mr. Rosenstein, he said, “I don’t think he did a lot to bolster our confidence in him.”
According to lawmakers and Mr. Rosenstein’s prepared remarks, the deputy attorney general offered little clarity about how related congressional inquiries may proceed in light of Mr. Rosenstein’s appointment on Wednesday of a special counsel, Robert S. Mueller III, to examine the possibility of collusion between President Trump’s associates and Russian officials.
The fact that Mr. Mueller’s inquiry is focused on possible crimes is almost certain to limit the cooperation of potential subjects of the investigation who might otherwise testify before Congress or share documents.
The decision by Mr. Comey to appear before the intelligence committee underscored the quandary of the competing claims between the imperatives of a special counsel and those of congressional committees.
Senator Lindsey Graham, Republican of South Carolina and a member of the Judiciary Committee, questioned Mr. Comey’s decision to testify, but then added that he believed he should also testify before his committee because it has oversight jurisdiction of the F.B.I.
The same sentiment seemed to be emerging in the House.
“Congress is going to want to look over the shoulder of this investigation,” said Representative Darrell Issa of California, a Republican who was an aggressive chairman of the House oversight committee during the Obama administration. “The executive branch will always try to limit that for fear it will contaminate potential criminal investigations, or leaks.”
“I don’t expect this to be any different,” he added.
Mr. Rosenstein instead delivered careful characterizations about the inquiry and deferred to Mr. Mueller’s autonomy as special counsel, and a pending investigation into Mr. Comey’s conduct by the Justice Department’s inspector general. He said that his memo had not been a legal brief, or a finding of official misconduct by Mr. Comey or “a statement of reasons to justify a for-cause termination.”
Representative Jackie Speier of California, a Democrat on the House Intelligence Committee, said Friday that Mr. Rosenstein had made it clear that Mr. Mueller would have “carte blanche authority,” but he also reassured lawmakers that he understood the role of Congress.
“I think he’s very respectful of the role that the Congress is playing in doing its investigation,” she said, “and the separate and distinct role that the Department of Justice is pursuing.”
Representative Elijah E. Cummings of Maryland, the House oversight committee’s top Democrat, said they would have “no problem” sitting down with Mr. Mueller to ensure the committee does not interfere in his investigation. They have a responsibility to secure the democratic process from foreign interference, he said.
“The Congress’s role really is to look forward to make sure this does not ever happen again,” Mr. Cummings said.
Mr. Rosenstein signed the legal order naming Mr. Mueller special counsel on Wednesday before informing Mr. Sessions or the White House of that decision. Democrats were simultaneously heartened by the selection of a respected former F.B.I. director and prosecutor to lead an investigation that they feared had been tarnished by Mr. Trump’s interference, while also concerned about the possibility of losing their grip on the information coming out of their own investigations.
Before the appointment of Mr. Mueller, House Democrats on Wednesday took procedural steps toward forcing a House vote to establish a separate, independent commission to conduct its own investigation, similar to the 9/11 commission. With little initial Republican support even for a special counsel and the process requiring majority support from the Republican-controlled House, it is considered a long shot. But some Democrats said the briefing with Mr. Rosenstein had only reinforced the need for such an independent body.
“After hearing everything that was said,” said Representative Adriano Espaillat, Democrat of New York, “there still is a need for an independent commission where the American people will be able to have more access to what happened.”
The New York Times has reported that Mr. Trump asked Mr. Comey for his “loyalty” during a private dinner and requested he drop the investigation into Michael T. Flynn, his former national security adviser, who is under scrutiny regarding his ties to Russia and Turkey.