A former FBI chief was tasked Wednesday with leading a beefed-up investigation into whether Donald Trump's team colluded with Russia to tilt the 2016 election in the president's favour.
Trump responded by once again denying any links to Moscow, but the appointment of a special counsel with sweeping powers dramatically raises the stakes in a crisis threatening to paralyze his presidency.
The Republican leader, who has struggled to shake off suspicions that Russia helped put him in the White House, has been accused of seeking to block the investigation by sacking FBI chief James Comey.
Under pressure to provide guarantees to Congress and the public that the Russia probe will continue unhindered, Deputy Attorney General Rod Rosenstein tapped Robert Mueller — a widely respected figure who headed the FBI for the decade after the 9/11 attacks — to take over the reins.
"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," Rosenstein said in a statement.
A New York-born Vietnam war vet aged 72, Mueller has a reputation as a tough lawman who once even stood up to a president.
He will head up the FBI's ongoing probe of "Russian government efforts to influence the 2016 presidential election and related matters," with the authority to prosecute crimes unearthed by the investigation.
Special counsels like the one named Wednesday to oversee the probe into Russia's alleged election interference are rare super sleuths with more power and independence than regular American investigators.
This time it is former FBI director Mueller who will take over the probe into the meddling as well as whether President Donald Trump's campaign team colluded with Moscow to tilt the election his way. The stakes are huge.
Unlike a US attorney, a special counsel has more leeway in carrying out a probe.
They are appointed when an investigation by a US attorney would present a conflict of interest or "under the circumstances, it would be in the public interest to appoint an outside Special Counsel to assume responsibility for the matter," says the law allowing for special counsels.
For instance, in 1999 Attorney General Janet Reno appointed Senator John Danforth to oversee a probe into the role of the FBI in a deadly assault in 1993 against the Branch Davidians sect in Waco, Texas.
A special counsel does not have to keep his or her superiors briefed on each step of the probe they are carrying out — even though the counsel does still answer to the Justice Department and thus, ultimately, to the president.
The attorney general or his or her deputy does not have to explain their criteria in choosing someone to be a special counsel, who can even come from outside government.
That is the case with Mueller, the former longtime FBI director who will resign from the law firm where he works to take on this job.
Mueller was named by deputy attorney general Rod Rosenstein, to whom he will report. Attorney General Jeff Sessions has recused himself from the Russia probe because he failed to state during his confirmation hearings that he had met with Russian officials.
A special counsel can issue subpoenas and ask for extra resources for a probe but must warn the attorney general or the deputy of important moves they plan to make in the investigation.
The attorney general can oppose a procedural act that the special counsel wants to make. And he or she can dismiss the counsel if they feel that individual has made a serious mistake or is in a situation of conflict of interest.
One of the best known special prosecutors was Archibald Cox, named to lead the Watergate investigation that led to Richard Nixon's resignation in 1974.
Nixon wanted Cox fired after he issued subpoenas for copies of taped conversations Nixon made in the Oval Office.
Attorney General Elliot Richardson refused to fire Cox, and resigned. His deputy William Ruckelshaus did the same in what came to be known as the "Saturday Night Massacre."
With inputs from AFP
Updated Date: May 18, 2017 10:50 AM