The New York Times reported on Wednesday that Trump had attempted to persuade Comey to drop a federal investigation into former national security adviser Michael Flynn, who resigned for misleading Vice President Mike Pence, and his possible ties to Russian Federation.
After being tapped on Wednesday to be the special counsel on the Trump-Russia probe, Mueller is endowed with sweeping prosecutorial powers and greater independence.
Illinois Democrat Dick Durbin echoed McCaskill, saying Rosenstein told lawmakers that he knew of Trump's intent the day before he wrote a document that the White House initially said was the main reason Comey was dismissed.
Several Republican senators asked Mr Rosenstein if the Senate Intelligence Committee could continue its own investigation into Russian interference in the 2016 election now that Mr Mueller has been appointed special counsel on the same matter.
There was no word on what that record might entail, a question many were likely to raise in light of Trump's recent warning to Comey that he had "better hope" there were no tapes of a discussion they'd had. He called the suggestion he had done anything potentially worthy of criminal charges "totally ridiculous".
"There is no collusion between certainly myself and my campaign, but I can always speak for myself, and the Russians-zero".
The news conference also came moments after Missouri Sen.
James Comey, the former Federal Bureau of Investigation chief whose firing by President Donald Trump has triggered uproar, has agreed to testify publicly about Russian interference in the 2016 elections, lawmakers have announced. Trump wrote, his anger boiling over.
During a speech at the Coast Guard Academy commencement Wednesday, an aggrieved Trump aired his mounting frustrations, declaring that "no politician in history, and I say this with great surety, has been treated worse or more unfairly".
Washington's intelligence agencies believe Moscow tried to tip November's USA presidential election in favour of Mr Trump. On Thursday, Reuters reported that Mr. Flynn and other advisers to Mr. Trump's campaign were in contact, via telephone and e-mail, at least 18 times with Russian officials and others with ties to the Kremlin in the last months of the presidential race.More news: Washington Capitals vs. Penguins live stream Game 7
More news: Ex-FBI Director Comey to testify in public Senate hearing
More news: Fired FBI chief Comey to testify publicly in Congress
USA stocks rallied back on Thursday after seeing their biggest drop in eight months the previous day on worries that the political turmoil could sideline Trump initiatives such as tax cuts that investors see as favouring economic growth. "It's special. The FBI has not had that special reputation with what happened in the campaign, what happened with respect to the Clinton campaign, and directly and indirectly to the more successful Trump campaign".
Lawmakers from both parties said they left the briefing on Capitol Hill with confidence in Rosenstein's decision, but also questions about what Mueller's probe would mean for separate investigations taking place in Congress. "I think it shows division, and it shows that we're not together as a country".
Rosenstein briefed senators on Thursday but made no public comments.
"You know the biggest problem for Republicans is not the firing of James Comey", Feehery said.
Afterward, Republican Senator Lindsey Graham told reporters that "everything he said was that you need to treat this investigation as if it may be a criminal investigation". Trump has insisted at times that the decision was his alone, but he also has pointed to the "very strong" recommendation from Rosenstein.
"There is mounting evidence of obstruction of justice", Blumenthal said, avoiding a specific question as to whether he was referring to President Trump or the firing of Comey.
The White House didn't learn of his appointment by Deputy Attorney General Rod Rosenstein until 30 minutes before it was publicly announced. "There has been no collusion", Trump said.
Trump fired Comey, who was leading the Justice Department's Russian Federation inquiry, last week.
As it stands, there are at least four congressional committees looking into roughly the same topic as Mueller: the House and Senate Intelligence Committees, the Senate Judiciary Committee and the House Oversight Committee.