As the chorus of calls grew louder for some kind of independent investigation of what's going on in Washington and as pushback stiffened from the White House, the announcement at 5 p.m. came with little warning or fanfare. Reporters were called to a no-camera Justice Department briefing where it was announced that Mueller was being named as special counsel.
Robert Mueller became director of the FBI one week before the 9/11 attacks, and was in that post for 12 years under two administrations: Republican George W. Bush and Democrat Barack Obama.
Since leaving government Mueller has been a law professor and in private practice.
Now he is pressed back into public service.
Rosenstein, who is acting Attorney General in the case because Attorney General Jeff Sessions recused himself, signed an order calling for a "full and thorough investigation of the Russian government's efforts to interfere in the 2016 presidential election...specifically any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump."
CLICK HERE to read the full order from Deputy Attorney General Rod Rosenstein.
Mueller's successor at the FBI, James Comey, had been in charge of the investigation until President Trump fired him last week. Now Mueller will lead the charge to determine whether there should be and will be criminal charges. His no-nonsense view of federal law enforcement has always been clear.
Rosenstein said in statement: "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. My decision is not a finding that crimes have been committed or that any prosecution is warranted. I have made no such determination. 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. ... a Special Counsel is necessary in order for the American people to have full confidence in the outcome. Our nation is grounded on the rule of law, and the public must be assured that government officials administer the law fairly. Special Counsel Mueller will have all appropriate resources to conduct a thorough and complete investigation, and I am confident that he will follow the facts, apply the law and reach a just result."
Mueller is resigning from his law firm in order to avoid any conflicts of interest with firm clients or attorneys.
President Trump released a statement in reaction, saying, "As I have stated many times, a thorough investigation will confirm what we already know - there was no collusion between my campaign and any foreign entity. I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."
Republican U.S. Representative Peter Roskam (IL-6) released a statement, saying, "The appointment of a special counsel to oversee the inquiry into Russian meddling in the U.S. presidential election is a welcome development. Former FBI Director Mueller is a man of the utmost integrity. I have complete confidence in his ability to conduct a thorough investigation, wherever the facts may lead."
Democrat U.S. Representative Mike Quigley (IL-5), who is on the House Permanent Select Committee on Intelligence, released a statement saying, "Former FBI Director Mueller is a highly respected public servant who has committed much of his public life to protecting this country. This appointment is a welcome step forward in our ongoing investigation and it is my hope that Mr. Mueller will continue to serve with the integrity that he displayed during his time with the FBI. We must follow the facts wherever they lead and that requires a prosecutor that is impartial, unbiased and committed to revealing answers critical to defending our national security and the public's trust. It also our responsibility as Members of Congress to hold Mr. Mueller accountable and to ensure that his investigation remains free from outside interference or obstruction."
Senate Intelligence Committee Chairman Richard Burr said the appointment of former FBI Director Robert Mueller as a special counsel is a "good decision" that "assures the American people that there's no undue influence" in the probe of Russian meddling in last year's election.
Burr, who heads the Senate investigation into the Russian activity and possible connections to associates of President Trump, said his committee will "continue to proceed forward" and the panel's job hasn't changed.
Burr told reporters, "I think this was a good decision."
House Democrats who have been pressing for a special counsel to examine possible collusion between Russia and the Trump campaign welcomed the news that Mueller would lead the investigation.
Minority Leader Nancy Pelosi said in a statement Wednesday that Mueller is "a respected public servant of the highest integrity."
She added that "a special prosecutor is the first step, but it cannot be the last. Director Mueller will still be in the chain of command under the Trump-appointed leadership of the Justice Department."
Rep. Elijah Cummings of Maryland, the top Democrat on the Oversight Committee, called Mueller a "solid choice," and commended Rosenstein for putting "our country and justice system first."
House Republicans had mixed reactions to the announcement.
Oversight Committee Chairman Jason Chaffetz of Utah said late Wednesday that Mueller is a "great selection. Impeccable credentials. Should be widely accepted."
But Rep. Peter King of New York expressed concern over the wide purview special prosecutors have. King said, "I'm worried with all special counsels because there's no control over them and they can abuse their power."
In the 1990s, Democrats insisted that independent counsel Kenneth Starr, who investigated former President Bill Clinton, overstepped his authority.
The Associated Press contributed to this report.