It was not clear whether the president was basing his tweet on direct knowledge, or on reports this week that special counsel Robert Mueller is examining whether he obstructed justice by firing Mr Comey last month amid the Russian Federation investigation.
Trump's young presidency has been battered by allegations - under investigation both by Congress and the FBI - that Russian Federation interfered to sway the 2016 election in his favor, in possible collusion with Trump's campaign team.
As part of his probe into possible obstruction, Mueller has requested interviews with senior intelligence officials about their conversations with Trump, a former senior intelligence official with knowledge of the discussions confirmed to NBC News. Now, ABC News reports that Deputy AG Rod Rosenstein, who replaced Sessions in supervising the Department of Justice's investigation into Trump-Russia collusion, knows that he might have to recuse himself, too.
USA intelligence agencies have concluded that Moscow interfered in last year's presidential campaign to try to tilt the vote in Trump's favour.
Aides said that the President had made a decision to take matters into his own hands and believed he was his own best defender in the escalating crisis surrounding the White House. "I can go around them", the tweet read. "Witch Hunt." Rosenstein wrote a memo for Trump outlining why the former Federal Bureau of Investigation director should be fired.
News of a possible Rosenstein recusal comes on the same day that President Trump issued a veiled slam against the deputy AG (while acknowledging that he is under investigation for obstruction of justice).
Mr Pence's office confirmed he had retained Richard Cullen, a former Virginia Attorney-General and U.S. attorney for the Eastern District of Virginia, to assist "in responding to inquiries" from Mr Mueller. "Nice", Mr Trump wrote in his first tweet.
Trump has said he is "100 per cent" willing to testify under oath on Comey meetings and tell the FBI Special Consul Robert Muller that he never asked FBI to stop investigating.
Mueller's investigation also includes the question of whether Trump tried to obstruct justice. Grassley announced Wednesday, to the consternation of some GOP colleagues, that the committee would investigate whether there was any "improper interference" with FBI investigations during the election or otherwise.