The Republican leader also lashed out at the Justice Department’s number two, the man tasked with organizing the probe.
The furious early morning barrage of tweets — his second in as many days — came as the special counsel investigating Russia’s influence over his election pieced together a high-caliber legal team and readied to begin interviews.
Trump is accused of firing FBI director James Comey over his refusal to steer the Russia investigation away from former national security advisor and Trump ally Mike Flynn.
The US president has denied trying to influence the investigation, but has acknowledged in an interview that Russia was on his mind when he dismissed Comey.
“I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt” he tweeted from the White House shortly before a day trip to Miami.
That appeared to be the first public confirmation that Trump is being investigated for obstruction of justice — and a digital salvo trained at Deputy Attorney General Rod Rosenstein, who wrote a memo criticizing Comey.
A source on Trump’s legal team attempted to clarify the missive, claiming he was reacting to media reports about the investigation rather than offering public confirmation.
Meanwhile, special counsel Robert Mueller — a respected former FBI director — has sought to beef up his investigatory firepower.
Peter Carr, a spokesman for Mueller, told AFP he now has “13 attorneys on board, with several more in the pipeline.”
That will only add to a sense of foreboding that pervades the White House, from the crammed collective workspaces of junior officials all the way to the Oval Office.
The widened Russia probe could have far-reaching repercussions for Trump’s presidency, transforming his closest aides into witnesses and sucking even more political oxygen out of the West Wing.
Trump was set to escape the Washington pressure cooker on Saturday. Accompanied by First Lady Melania, he will make his first trip to the Camp David presidential retreat in Maryland.
A weekend at the rustic mountain getaway is a far cry from the president’s normal routine of jetting off to one of his lavish resorts, mainly Mar-a-Lago in Florida.
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On Wednesday, Vice President Mike Pence took what he later described as a “very routine” step of hiring outside counsel to represent him.
Pence tapped far-from-average lawyer Richard Cullen, who litigated the 1980s Iran-Contra scandal, the Watergate affair and the 2000 vote recount in Florida.
As the legal rope has tightened, Trump’s allies have gone on the offensive, questioning Mueller’s credibility and floating the idea he may be fired.
Trump’s apparent attack on Rosenstein also raised further questions about whether he will stay in his position or recuse himself from the investigation.
“As the deputy attorney general has said numerous times, if there comes a point when he needs to recuse, he will. However, nothing has changed,” said Ian Prior, a Justice Department spokesman.
Top Democratic Senator Dianne Feinstein expressed concern that Trump may try to fire both Mueller and Rosenstein, warning “he’s in for a rude awakening” if he thinks he can shut down the investigation.
“Even his staunchest supporters will balk at such a blatant effort to subvert the law,” Feinstein said.
Trump also lashed out at the media, on a day that aides hoped would be focused on his decision to undo some of Barack Obama’s detente with Cuba.
“After 7 months of investigations & committee hearings about my ‘collusion with the Russians,’ nobody has been able to show any proof. Sad!” Trump tweeted.
“The Fake News Media hates when I use what has turned out to be my very powerful Social Media – over 100 million people! I can go around them.”
Trump’s young presidency has been battered by allegations — under investigation both by Congress and the FBI — that Russia interfered to sway the 2016 election in his favor, in possible collusion with Trump’s campaign team.
The president has long vehemently denied any collusion with Moscow.