The US president stands accused of seeking to stall the politically-explosive probe following his shock dismissal of the FBI chief James Comey, and allegations that he asked Comey to drop his investigation of a former aide.
Deputy Attorney General Rod Rosenstein yesterday tapped Robert Mueller -- a widely-respected figure who headed the FBI for the decade after the 9/11 attacks -- to take over the FBI's probe of "Russian government efforts to influence the 2016 presidential election and related matters."
Capping days of political drama in Washington, the move came as pressure mounted in Congress for an independent probe into ties between Trump's campaign and Moscow, which US intelligence chiefs say interfered to tilt the election in the Republican's favor.
A special counsel is empowered to conduct the investigation independent of the Justice Department hierarchy, with a dedicated staff of his choosing. The counsel is not required to consult with or keep informed the attorney general or deputy attorney generals on the course of the probe.
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Rosenstein's order came a week after he played a key role in Trump's firing of Comey, who had overseen the FBI investigation into Russia's election interference since last July.
The deputy attorney general penned a letter criticizing Comey's handling of the probe into Hillary Clinton's emails, which provided the White House with the rationale for firing Comey -- and raised questions about Rosenstein's own ability to remain politically independent.
His boss, Attorney General Jeff Sessions, was forced to recuse himself from the investigation in March due to his own undisclosed contacts with the Russian ambassador, Sergey Kislyak.
Trump's alleged pressure on Comey -- denied by the White House -- has exposed the president to accusations of obstructing justice.
Mueller was director of the FBI from 2001 to 2013, a period when he was forced to shake up a huge bureaucracy blamed for missing evidence that could have prevented the September 11, 2001 attacks.
During his tenure he served both Republican and Democratic presidents, and is highly respected by both parties.
Trump has consistently rejected any suggestion of collusion between his camp and Moscow as "fake news" and complained in a speech on Wednesday that he had been treated "more unfairly" than any US leader in history during his fledgling presidency.