"Wow, that's news to me. He is a well-respected law enforcement professional," Sen. John Cornyn, the Senate's No. 2 Republican, told reporters Wednesday evening when asked about the turn of events. "That's the call of the deputy Attorney General. It's not our call. It's his call. He previously said he didn't see the need and until there was a demonstrated need he wasn't interested. This is a development I wasn't aware of."
According to members and GOP and Democratic aides that spoke to CNN, many members of leadership weren't even in the loop that the announcement was coming, but one aide noted that the news was "helpful" in relieving some pressure on GOP lawmakers.
The daily pounding lawmakers were taking was beginning to take its toll.
For Republicans from swing districts, the news provided some hope that the GOP might now be able to get back to focusing on a legislative agenda instead of one that catapulted them from crisis to crisis.
"It's good that we now have a focal point of somebody that we all trust," said former House Oversight Chairman Darrell Issa. "Multiple people, starting in February when I called for it, have said we needed this independent counsel, we needed the ability to know that we had a point of contact who had the resources."
Rep. Barbara Comstock, a Republican from Virginia who will face a tough re-election in 2018, said that it was the "right thing to do."
New Jersey Rep. Leonard Lance, a Republican, said on on CNN's "Erin Burnett OutFront" that he had no reservations about Mueller's appointment and predicted the investigation wouldn't end quickly. He said he supported Mueller going wherever the investigation needed to, including reviewing the President's tax returns.
"I support the independence of the special counsel," Lance said.
Senate Minority Leader Chuck Schumer said in a statement that "a special counsel is very much needed in this situation and Deputy Attorney General Rosenstein has done the right thing."
A senior GOP leadership aide told reporters Wednesday that Rosenstein will brief all House members Friday in a classified meeting. Rosenstein was already scheduled to speak to all senators on Thursday afternoon for a similar briefing.
In initial conversations with top congressional sources, there was a relief about the decision--at least in the short term-- as sources believed the announcement would take the pressure off Republicans to create a 9/11 type commission or even a select committee.
Schumer joined other Democrats in expressing confidence that Mueller was "exactly the right kind of individual for this job."
"I now have significantly greater confidence that the investigation will follow the facts wherever they lead," Schumer continued in his statement.
New York Rep. Joe Crowley, Democratic caucus chairman, also said on CNN's "Erin Burnett OutFront" that Rosenstein's move was a step in the right direction, but that there might still be a need for an independent commission "down the road."
Referencing a similar sentiment from House Minority Leader Nancy Pelosi, Crowley praised Mueller.
"Mueller comes with great, bipartisan credentials," Crowley said. "He's highly regarded on both sides of the aisle."
Senate Majority Leader Mitch McConnell said in a statement that the appointment of the special counsel "confirms that the investigation into Russian intervention into our election will continue, as stated last week by Acting FBI Director Andrew McCabe"
House Speaker Paul Ryan also said that he supported the move and that the investigation would continue in the House.
Not everyone, however, was as enthusiastic.
Rep. Peter King, a Republican from New York, told reporters that he was "fine" with the decision, but thought it was unnecessary.
King argued it was probably done in response to the hysteria of the week to "calm down the media ... throw raw meat to the wolf pack."
Sen. Chuck Grassley, the Chairman of the Senate Judiciary Committee demurred when asked about whether it was the right move or not.
"It doesn't matter if I think it's the right move or not it's something they got the authority to do and we have to accept," Grassley said.
Democrats had been calling for Rosenstein to appoint a special counsel for months, but those demands had only intensified last week after news broke of Comey's firing and then allegations surfaced that Trump had asked Comey to let an investigation go into his former national security adviser Michael Flynn, according to a Comey memo.
Still, many Republicans say that the special counsel won't have much effect on how they look at the Russia investigation.
Rep. Mike Conaway, who is running House intelligence committee Russia investigation, said that a special counsel won't impact his committee's investigation. His panel after all doesn't have prosecutorial tools so he said it shouldn't interfere.
"We don't have those tools, and I'm not in competition with the criminal side," Conway said noting he too didn't get a heads up.
On the Senate side, the leader of that investigation cheered the decision.
"This assures everybody that one of the most reputable individuals is overseeing the review," Senate intelligence committee Chairman Richard Burr said.