Rosenstein appointed former Federal Bureau of Investigation head Robert Mueller as the special counsel to investigate the Trump administration and presidential campaign for collusion with Russian Federation to interfere with November's election.
Sen. Lindsey Graham (R-SC) came out of a Senate-wide briefing Thursday by the US deputy attorney general with the impression that the federal probe into Russia's interference in the USA election has entered criminal territory.
Sen. Lindsey Graham said Thursday he believes the Justice Department's Russian Federation probe is "now considered a criminal investigation", comments he made following the all-senators' briefing with deputy Attorney General Rod Rosenstein.
Trump himself, in a statement right after the appointment late Wednesday, said merely, "A thorough investigation will confirm what we already know - there was no collusion between my campaign and any foreign entity".
Mr Trump said in a speech earlier on Wednesday that no politician in history "has been treated worse or more unfairly".
At a press conference later on Thursday, Trump said, "I respect the move but the entire thing is a witch hunt. There is no collusion".
Despite initially opposing the appointment of an independent counsel, House Speaker Paul Ryan said the development "helps assure people and the justice department that they're going to go do their jobs independently and thoroughly, which is what we've called for all along".
According to sources familiar with the matter, Trump asked Comey to end the investigation into former national security adviser Michael Flynn, a request documented in a memo written by the former FBI director.
He said Rosenstein didn't tell lawmakers who told him to write the memo with the rationale for ousting Comey.
By Wednesday evening, a Republican source said that the move effectively shut down Congress' intense digging into Comey and his conversations with Trump. "Because you look at all of the people on the Democratic side, not only the Republican side, that were saying such awful things about Director Comey".
"I believe it hurts our country terribly", Trump told network anchors during a luncheon Thursday afternoon at the White House.
While the investigation by the Senate Intelligence Committee will continue, several lawmakers said the panel's role may be reduced with the appointment of a special counsel. Republicans on Capitol Hill hoped the same, reasoning that the appointment of a special counsel could free them to work on a major tax overhaul and other matters without constant distractions. But the revelations about the timeline dovetail with more recent statements from Trump that he planned to fire Comey regardless of any DOJ recommendation. In addition to his investigatory and prosecutorial abilities with relation to the interference in the election, as set out by Rosenstein, Mueller is also granted the capacity to pursue crimes committed in the course of his probe.
Trump has repeatedly slammed the FBI and congressional investigations as a "hoax" and blamed disgruntled officials at intelligence agencies for leaking information related to the probes.
The GOP has largely downplayed the effect the turmoil at the White House has had on their legislative ambitions.