President Donald Trump confirmed Friday he was under investigation and appeared to take aim at a senior Justice Department official, in a tweet that seemed to encapsulate his frustration with the ongoing focus on Russia's involvement in the 2016 election.
Special counsel Mueller - a respected former Federal Bureau of Investigation director - was also bringing in legal firepower to investigate whether there was collusion between Trump's team and Russian Federation to fix the 2016 election or an attempted cover-up.
"I'm growing increasingly concerned that the president will attempt to fire not only Robert Mueller, the special counsel investigating possible obstruction of justice, but also Deputy Attorney General Rosenstein who appointed Mueller", the Democratic senator, who is also a member of the Senate Intelligence committee, said in a statement. The President has been criticizing the special counsel appointment as the "single greatest witch hunt" in the history of US politics.
Trump wrote that the investigation has not "been able to show any proof", an allegation that he assessed with one of his signature Twitter catchphrases: "Sad!"
Although he didn't name anyone, Trump appeared to be pointing the finger at Rod Rosenstein, the deputy attorney general who began overseeing the Russian Federation investigation after Attorney General Jeff Sessions recused himself from it.
Comey said he typed notes describing the conversations because he was anxious Trump "might lie" later about them. Trump cited the memo in firing Comey.
Trump advisers and confidants describe the president as increasingly angry over the investigation, yelling at television sets in the White House carrying coverage and insisting he is the target of a conspiracy to discredit - and potentially end - his presidency. Reports have alleged that Trump asked both men to publicly quash the credibility of the Russian Federation investigation.
In this last tweet, Trump was referring to a memo written by Rosenstein that was intensely critical of Comey and implicitly recommended his removal.
"He's driving this", the White House official said, speaking on condition of anonymity to discuss West Wing internal deliberations. "I can go around them".
"I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director!"
He's been advised of the legal ramifications from making these presidential statements on Twitter, but he and at least a few advisers have come to believe the political fight is more urgent.
On Thursday Trump derided a "witch hunt" against him, led by some "very bad" people.
The transition official said the organization has also separately asked the General Services Administration to preserve records from the Trump transition that were transferred to its facilities after Trump's inauguration.
A day earlier, Trump had questioned why his general election rival Hillary Clinton was not being investigated.