-- The news that the Department of Justice has appointed a special counsel to investigate Russia's interference in the 2016 presidential election came as a bombshell in Washington.
The White House was informed of the decision less than an hour before the news was publicly announced, and many in the FBI had no notice at all, sources told ABC News.
"As I have stated many times, a thorough investigation will confirm what we already know – there was no collusion between my campaign and any foreign entity," President Donald Trump said in a statement. "I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."
On the Hill, a number of lawmakers from both sides of the aisle praised the selection of former FBI Director Robert Mueller, who also served as a U.S. attorney.
Republican Rep. Jason Chaffetz of Utah -- who earlier today invited ousted FBI Director James Comey to testify before the House Oversight and Government Reform Committee on issues related to the "FBI's independence" -- lauded Mueller's "impeccable credentials" and said he "should be widely accepted."
One of the first congressional Republicans to call for the appointment of a special prosecutor to address Russia's alleged election meddling, California Rep. Darrell Issa said today, "It's time to get to the bottom of this."
"I've been pressing the DOJ to take this step for nearly 3 months because Americans deserve nothing less than the truth," he added in a statement. "I have faith that Robert Mueller will provide the independence necessary to be sure this investigation is conducted with the trust and confidence of the American people."
Democratic Sen. Dianne Feinstein of California, the ranking member of the Senate Judiciary Committee that is currently investigating possible collusion between Russia and the Trump campaign said in a statement the announcement was "a good first step to get to the bottom of the many questions we have had about Russian interference in our election and possible ties to the president."
"Bob ... is respected, he is talented and he has the knowledge and ability to do the right thing," Feinstein said.
Her Republican counterpart on the Judiciary Committee, chairman Sen. Chuck Grassley of Iowa, praised the Justice Department's decision.
"I have a great deal of confidence Deputy Attorney General Rosenstein and I respect his decision," Grassley said. Because Attorney General Jeff Sessions previously recused himself from the investigation, it was Rosenstein, not Sessions, who announced the special counsel. "At the end of the day, we need a public accounting of what went on to restore faith in government," Grassley added.
The chair and vice chair of the Senate Committee on Intelligence, which is also investigating the Trump/Russia issue, came together for a joint statement:
“The appointment of former FBI Director and respected lawyer Robert Mueller as special counsel for the Russia investigation is a positive development and will provide some certainty for the American people that the investigation will proceed fairly and free of political influence," Sens. Richard Burr, R-North Carolina, and Mark Warner, D-Virginia, said in their statement, noting their committee would continue its own investigation.
Sen. Tim Kaine, D-Virginia, Hillary Clinton's running mate in 2016, called the appointment "a good move" on Twitter. "Now let's get some answers," he added.
Clinton's former spokesperson, Brian Fallon, also weighed in, saying Mueller "has Jim Comey's independent streak, minus Comey's lust for the spotlight." During the campaign, Fallon blasted Comey's decision to publicly announce the FBI was reopening the investigation into Clinton's use of a private email server while secretary of state.
Democratic Sen. Jeff Merkley, D-Oregon, called Mueller's appointment "a victory for all Americans who believe in the integrity of the rule of law" and insisted the investigation "must be given the full resources and independence it needs to succeed."
Speaker of the House Paul Ryan, R-Wis. -- who today stood by President Trump even as talk of Comey's memos about possibly inappropriate conversations swirled -- said he welcomed Mueller's appointment.
"My priority has been to ensure thorough and independent investigations are allowed to follow the facts wherever they may lead. That is what we’ve been doing here in the House," Ryan said in a statement. "The addition of Robert Mueller as special counsel is consistent with this goal, and I welcome his role at the Department of Justice. The important ongoing bipartisan investigation in the House will also continue."
Minority leader Nancy Pelosi, D-California, noted she was "pleased" by the Justice Department's designation of Mueller, but said the appointment "is the first step, but it cannot be the last. Director Mueller will still be in the chain of command under the Trump-appointed leadership of the Justice Department. He cannot take the place of a truly independent, outside commission."
"This takes the politics out of it, hopefully. This has gotten too political," Rep. Adam Kitzinger, R-Illinois, told reporters. "I think it's a good move and hopefully something that will give the American people some peace that we'll get to the bottom of this."
According to the Justice Department, Mueller -- who is resigning from his law firm to avoid any conflicts of interest -- will have all of the authorities of a U.S. attorney, including the ability to take the matter before a grand jury and the ability to issue subpoenas. Although he has wide latitude to hire his team, Mueller's budget will be subject to approval by Roseinstein.
Today's news comes on the heels of a series of startling revelations this month: First, Trump's announcement he had fired FBI director James Comey, who was leading the Russia probe, then the news that Trump disclosed classified intelligence to Russian officials, and finally, reports that Trump asked Comey to ease up on the investigation into former national security adviser Michael Flynn, who was fired after he mislead the vice president about the nature of his discussions with Russia's Ambassador to the U.S. Sergey Kislyak.
President Trump has labeled allegations of collusion with Russia "a total hoax."
ABC News' Mike Levine, Jonathan Karl, Ali Weinberg, Benjamin Siegel, MaryAlice Parks, Jack Date, Arlette Saenz, and Fergal Gallagher contributed to this report.