Some senators say they're anxious the Justice Department's appointment of a special counsel to oversee the Russian Federation investigation could effectively halt congressional probes into the matter.
A defiant President Donald Trump has lashed out at what he called "the greatest witch-hunt of a politician in American history" after a special counsel was appointed to oversee the FBI's investigation into Russia's alleged efforts to influence the 2016 presidential election.
Senators said that Rosenstein made clear that he has ceded all authority over the investigation over to Mueller. Susan Collins, a Republican, also confirmed similar details revealed during the briefing.
Trump claimed that the report on Comey's memo was not true.
Trump has cited Rosenstein's memo on Comey as contributing to his decision to fire him, while Democrats have criticized Rosenstein for agreeing to write it.
Initially it was Rosenstein's memo - critical of Comey's handling of the Hillary Clinton email scandal past year - that was put forward as the justification for the dismissal.
"I think this was a great move and he (Deputy U.S. Attorney General Rod Rosenstein) picked the right guy", he told KTAR News 92.3 FM's Bruce St. James and Pamela Hughes on Thursday. Trump attached both documents to his letter informing Comey of his removal.
Comey announced in March that the Federal Bureau of Investigation was also investigating Russian hacking during the 2016 election, including potential collusion between the Trump campaign and the Kremlin.
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Brazil's stock market fell by 10% in early trading this morning, wiping out nearly all of the year's gains in a matter of minutes. Now "those efforts may come to nothing", he warned, calling for a "full and very rapid" investigation at the Supreme Court.
South Carolina Sen. Lindsay Graham took it a step further, saying that the Justice Department's look into the Trump campaign's possible Russian Federation ties is "now considered a criminal investigation".
Sen. Dick Durbin, D-Illinois, said Rosenstein told the full Senate he was not pressured into writing the memo, but did so after learning of the president's decision to fire Comey.
"It was a counterintelligence investigation before now", says Graham.
"I would be very discouraged if somehow this new special prosecutor would preclude Jim Comey from testifying in public before our committee", he said.
The appointment won Rosenstein wide praise from Republicans and Democrats.
"I think that's an open question", said Democratic Senator Chris Coons, when asked if Comey would appear before Congress, adding that it remains to be seen "how ongoing congressional investigations will be coordinated with the special counsel".
A number of lawmakers exited the meeting stressing that Mueller's probe, while appropriately diving in to all possible Trump-Russia ties, may make it more hard for current congressional investigations to access vital intelligence.