Updated at 9:15 p.m. ET
The Justice Department is appointing former FBI Director Robert Mueller as a special counsel to oversee the growing probe into Russian meddling in the 2016 election and possible ties to associates of President Trump.
"In my capacity as acting Attorney General, I determined that it is in the public interest for me to exercise my authority and appoint a Special Counsel to assume responsibility for this matter," Deputy Attorney General Rod Rosenstein said in a statement.
"My decision is not a finding that crimes have been committed or that any prosecution is warranted. I have made no such determination," Rosenstein continued. "What I have determined is that based upon the unique circumstances, the public interest requires me to place this investigation under the authority of a person who exercises a degree of independence from the normal chain of command."
"I accept this responsibility and will discharge it to the best of my ability," Mueller said Wednesday evening.
Trump reiterated in a statement after Mueller's appointment that there was no collusion between his campaign and Russia, which "a thorough investigation" would confirm.
"I look forward to this matter concluding quickly," the president said. "In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."
Comey firing is backdrop for Mueller appointment
The appointment of Mueller — who is widely respected on both sides of the aisle -- comes after growing outcry, mostly from Democrats, amid fallout of President Trump's firing of FBI Director James Comey last week. While the White House initially insisted the dismissal was precipitated by Comey's mishandling of the investigation into Democratic presidential nominee Hillary Clinton's emails — outlined by Rosenstein in a memo — Trump later told NBC's Lester Holt that the Russia investigation factored into his decision.
That memo from Rosenstein came under scrutiny following Comey's ouster. Senate Minority Leader Chuck Schumer said in April that Rosenstein had assured him he would appoint a special counsel "if required." Last week, Schumer said if Rosenstein didn't follow through on that, "every American will rightly suspect that the decision to fire Director Comey was part of a cover-up."
Two sources close to Comey told NPR that Trump asked Comey to scuttle an investigation into former national security adviser Michael Flynn the day after Flynn resigned. Flynn stepped down after reports he had misled Vice President Pence about his conversations with the Russian ambassador. The White House denies that Trump made the request to shut down the probe.
A Comey associate says Comey wrote a memo after his encounter with the president, and congressional committees investigating the Russia ties have asked to see the memo and other related documentation. The House Oversight and Government Reform Committee has also asked Comey to testify next week.
Rosenstein has the authority to appoint a special counsel since Attorney General Jeff Sessions has recused himself from any part in the investigation. Sessions said in March he would step back, after reports he had met twice with the Russian ambassador during the campaign — contacts he insisted were innocent.
As special counsel, Mueller will have full authorization to direct the Russia investigation, including any links or coordination between the Russian government and individuals associated with Trump's campaign and any other matters. He can only be fired by Rosenstein, only with cause, and with notice to Congress. He is authorized to prosecute federal crimes that may arise from the probe.
As NPR's Scott Horsley noted last week, the Justice Department has typically appointed special counsels instead of special prosecutors "to investigate suspected criminal activity when an investigation by the Justice Department itself might pose a conflict of interest. Because these counsels are appointed by — and answer to — the attorney general, they have less formal independence than independent counsels."
Sen. Patrick Leahy, D-Vt., argued that Mueller's investigation should extend to the circumstances surrounding Comey's firing.
"I have been pressing the Justice Department to take this step for months. But this must only be a first step," Leahy, a senior member of the Judiciary Committee, said in a statement. "No doubt this investigation should extend to the circumstances that led to the President's abrupt dismissal of James Comey, and to other critical matters that arise. This is important and urgent work."
Mueller praised as honest broker, "not directed by politics"
Mueller, who preceded Comey at the FBI, had a 12-year stint at the agency after being unanimously confirmed by the Senate in 2001 — just the week before the Sept. 11 terrorist attacks. His tenure leading the bureau was defined by what he did to adapt to the new threats posed to America by terrorism, and he was asked by then-President Barack Obama to stay on beyond the typical 10-year term for two additional years, which Congress approved.
"I had been a prosecutor before, so I anticipated spending time on public corruption cases and narcotics cases and bank robberies and the like, and Sept. 11 changed all of that," he told NPR in 2013 as he was stepping down.
Mueller moved 2,000 agents from criminal investigations into counterterrorism and national security in his time leading the FBI. Airline-related terrorism was a theme for Mueller throughout his career even before that, however; as a prosecutor he spent years working on an investigation into the bombing of Pan Am Flight 103, which exploded over Lockerbie, Scotland, in 1988.
Since retiring from the FBI in 2013, he has been working as a partner for the law firm WilmerHale, which confirmed Wednesday night that Mueller had resigned from the firm immediately upon his appointment to the new post.
The firm said Aaron Zebley, who worked for Mueller at the FBI, and James Quarles, who was previously an assistant special prosecutor on the Watergate Special Prosecution Force, also resigned from WilmerHale and are expected to join Mueller's investigation.
Former George W. Bush administration Attorney General John Ashcroft, who served with Mueller, told NPR's Ari Shapiro, "I don't know a person more dedicated to the concept and ideal of justice" than Mueller.
"He's not directed by politics," Ashcroft said. "Bob is the kind of guy who knows how to call balls and strikes."
Many Democrats were quick to offer praise for Mueller, too. House Minority Leader Nancy Pelosi said she was "pleased" that the Justice Department had decided to appoint a special counsel and called Mueller "a respected public servant of the highest integrity."
Senate Judiciary Committee ranking member Dianne Feinstein, D-Calif., called Mueller "a fine U.S. attorney, a great FBI director and there's no better person who could be asked to perform this function. He is respected, he is talented and he has the knowledge and ability to do the right thing."
Maryland Rep. C.A. "Dutch" Ruppersberger said the move "brings back credibility to the system to conduct an investigation." Ruppersberger, a former top Democrat on the House Intelligence Committee, worked with Mueller for years. He added, "It says to me that Rosenstein — he's an ethical, honest person — made the right decision, and what's right for America, not right for one person."
GOP congressional leaders reiterated that their chamber's own investigation, led by the House Intelligence Committee, would continue alongside Mueller's new responsibilities.
House Speaker Paul Ryan said Mueller's appointment was "consistent" with the House's own independent investigation into Russia, "and I welcome his role at the Department of Justice. The important ongoing bipartisan investigation in the House will also continue."
Senate Majority Leader Mitch McConnell simply said that Mueller's appointment "confirms that the investigation into Russian intervention into our election will continue, as stated last week by Acting FBI Director Andrew McCabe. The Senate Select Committee on Intelligence will also continue its investigation into this matter."
"I hear he's a no-nonsense guy," said Rep. Mark Walker, R-N.C., a conservative leader in the House who welcomed the decision. "It seems pretty positive at this point."
Like many Republicans, Rep. Lamar Smith, R-Texas, did not believe a special counsel was necessary, but he praised Mueller as the right choice if there is going to be one.
"I think former Director Mueller is a great choice," Smith said. "He has served in both Republican and Democratic administrations, he has a reputation for integrity, and I think he'll be well-received."
White House press secretary Sean Spicer had said on Monday there was "no need for a special prosecutor. And I think if you even look at what Acting Director McCabe said last week [in a Senate Intelligence hearing], he made it very clear that they had the resources that they need and that the work continues."
Meanwhile, the president is interviewing candidates to replace Comey as FBI director, and a nominee could be named by Friday. Trump was to meet with four candidates at the White House on Wednesday, including former Sen. Joseph Lieberman of Connecticut, a Democrat turned independent; and former Oklahoma Gov. Frank Keating, a Republican. McCabe was also set for a White House interview, along with Richard McFeely, a former FBI official. Two other political candidates for the job — Texas Sen. John Cornyn and South Carolina Rep. Trey Gowdy — took themselves out of the running.
Susan Davis, Scott Horsley and Miles Parks contributed to this report.