"This is the single greatest witch hunt of a politician in American history" he tweeted.
President Donald Trump later acknowledged that he had already thought about dismissing Comey and had been perturbed by "this Russian Federation thing", fueling criticism that Rosenstein's memo merely served as a pretext so the president could fire Comey amid an aggressive investigation into his campaign.
"Mr. Mueller will tell us what we can get", Graham said, referring to former FBI Director Robert Mueller, who Rosenstein appointed as special counsel on Wednesday.
President Donald Trump on Thursday said there was no collusion between his campaign and Russian Federation, while adding the caveat that he can only speak for himself, and denied ever asking FBI Director James Comey to back off his agency's investigation into former national security adviser Michael Flynn. "As to Mr. Comey, the former director of the Federal Bureau of Investigation, coming before the committee, if I were Mr. Mueller I would jealously guard the witness pool". Frenkel worked previously in the Office of Independent Counsel - a type of special prosecutor no longer in use.
"The special counsel has no legal or other obligation to interface or interact at all with Congress about the substance of the investigation", Frenkel said. He has served presidents of both political parties and, after taking the director job days before the September 11 attacks, oversaw the FBI's terrorism-fighting efforts over the next decade.
Sen. Marco Rubio commented on President Trump's statement that the situation is a "witch hunt" as well saying, "He's entitled to his opinion but 'we are a nation of laws'".
Democratic Senator Amy Klobuchar responded, "This is a truth hunt".
Trump later told news anchors at the White House that Mueller's appointment was a "very, very negative thing", adding, "I believe it hurts our country terribly, because it shows we're a divided, mixed-up, not-unified country".
Cheney suggested that concern over the twitter account was because it allowed Trump to circumvent the press role as government watchdogs.
But why Rosenstein's briefing needed to happen in a room designed for classified briefings is still unclear.
White House officials cast Rosenstein as the prime person behind the decision to fire Comey, even though Trump had already chose to terminate the director. He is a key figure in the Trump-Russia investigation.
Trump told Rosenstein that Comey "had to go", said Illinois Democrat Dick Durbin after leaving the all-senators meeting.
"This shuts the whole thing down", said one Republican source, speaking on Congressional efforts to investigate Comey's discussions with Trump.
Senator Chris Murphy, a Connecticut Democrat, said Rosenstein wasn't prepared to outline other circumstances surrounding the firing of Comey out of his belief that it could come within the territory of Mueller's investigation.
Trump went on to dismiss as "totally ridiculous" the notion that he himself may have committed a prosecutable - or even impeachable - offence in recent months, as argued by some critics who suspect him of obstructing the FBI's probe. Committees in both houses of Congress have invited Comey to testify publicly.
Asked about the potential that there had been obstruction of justice, Republican House of Representatives Speaker Paul Ryan told reporters the special counsel will "follow the facts where ever they may lead" and that "it is premature to prejudge anything at this point".
Flynn is accused of misleading Vice President Mike Pence about conversations he had with the Russian ambassador during the Trump transition. One user, Republican Tears, answered it by reminding Trump the long line of USA presidents who had experienced worse than him.
Rosenstein did not notify White House counsel Donald McGahn of his special counsel decision until 5:30 p.m., the same time Justice Department officials were briefing reporters and 30 minutes before the news became public.