White House press secretary Sarah Sanders responded quickly to a Friday New York Times report claiming that President Donald Trump's firing of former FBI Director James Comey led officials to begin investigating "whether he had been working on behalf of Russian Federation against American interests".
Mueller's probe has brought indictments against 34 people including Trump's former campaign chairman, Paul Manafort; Trump's first national security adviser, Michael Flynn, as well as a series of Russian intelligence officers and Kremlin-connected officials.
An American presidential campaign chairman handing over of internal polling data to a corporate associate of a foreign power is unusual, at best.
"I don't know if there's any time in our lifetime or the history of the country where federal law enforcement looked down to the White House ... and thought the actions of the president might threaten USA national security".
FBI agents and senior officials began to suspect connections between Trump and Russian Federation during the 2016 campaign but pushed off an investigation partially because they were unsure how to execute such a massive and sensitive operation, sources told the Times.
The Times reported that FBI investigators looked into whether Trump's actions could be considered a threat to national security.
Mueller is believed to be investigating whether Comey's firing and other actions amount to obstruction of justice by the president.
This is the first time a sitting US president has been investigated by the Federal Bureau of Investigation on suspicion of acting as an agent for a hostile foreign power.
Also fueling the FBI's concerns was Christopher Steele's "dirty dossier" of unsubstantiated allegations, which had been funded by Democrats but at that point was justifying probes across the Justice Department.
"When I did this, now I said to myself, 'You know, this Russian Federation thing with Trump and Russian Federation is a made-up story".
Trump and his allies have repeatedly criticized Mueller's investigation, calling it a "witch hunt" and questioning the political motivations of his investigators. She also disputed that Trump had ever been soft on Russian Federation.