Rosenstein's 2:30 p.m. briefing with the Senate was scheduled before he announced late Wednesday that he was appointing Robert Mueller, a former prosecutor who served as FBI director from 2001 to 2013, to take over the Russia investigation as special counsel.
To emphasize the independence of his decision, Rosenstein did not notify White House Counsel Donald McGahn of the appointment until 5:30 p.m., the same time Justice Department officials were briefing reporters and 30 minutes before the news became public.
Trump tweeted early Thursday morning that he was the victim of a "witch hunt" and expressed anger that a special counsel hadn't ever been appointed to investigate Hillary Clinton or former president Barack Obama for their "illegal acts." (He misspelled "counsel" as "councel.")
"With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special councel appointed!" Trump tweeted. "This is the single greatest witch hunt of a politician in American history!"
Rosenstein will most certainly be asked by senators about his decision to launch an independent investigation, as well as the circumstances surrounding the memo he wrote about Comey .
After the Senate briefing was announced Monday by a spokesman for Senate Majority Leader Mitch McConnell, R-Ky., Senate Minority Leader Charles Schumer, D-N.Y., said in a statement that he hoped senators on both sides of the aisle would "use this opportunity to seek the full truth" about Comey's firing.
Last week, in his memo about Comey, Rosenstein wrote that the FBI director had violated longstanding Justice Department practices in his handling of FBI investigation into Hillary Clinton's use of a private email server as secretary of state. Principal Deputy White House press secretary Sarah Huckabee Sanders pointed to Rosenstein's memo as the reason for Trump's firing, saying that Comey had committed "atrocities" in overseeing the FBI's investigation into Clinton.
But, according to a person close to the White House, Rosenstein was upset about the narrative that emerged from the White House the evening of May 9. That telling cast Rosenstein as the prime mover of the decision to fire Comey, even though Trump late stated that he had already decided to fire him before asking Rosenstein for the memo. Rosenstein threatened to resign from the Justice Department because of the explanation that White House officials were giving reporters about why the firing happened.
By Wednesday, White House officials had backed off blaming Rosenstein for the firing and the next day Trump contradicted his own officials and told NBC News that the decision to fire Comey was his alone and he was thinking of "this Russia thing with Trump" when he made it.
Rosenstein may have blunted some of the criticism of his actions in the last week with his special counsel announcement Wednesday. Both Democratic and Republican lawmakers praised Rosenstein's appointment of Mueller to oversee the probe into Russian meddling in last year's presidential election and possibly investigate whether the president or anyone at the White House has interfered with the investigation.
Rep. Jason Chaffetz, R-Utah, chairman of the House Oversight and Government Reform Committee, cheered Rosenstein's choice on Twitter, writing: "Impeccable credentials. Should be widely accepted."