President Donald Trump in the Oval Office after an interview with Reuters at the White House. Thomson Reuters President Donald Trump's decision Tuesday to fire FBI Director James Comey, who was leading an investigation into whether Trump's campaign colluded with Russia during the 2016 election, was quickly met with scrutiny on both sides of the political aisle.

"In any normal administration, firing the director of the FBI during an investigation of the administration would be viewed as suicidal," said Robert Deitz, a former top lawyer for the CIA and the National Security Agency who served under Presidents Bill Clinton and George W. Bush.

"This of course is not a normal administration," he added. "But no matter what, this will create a firestorm that will disturb even Trump loyalists on the Hill."

Most Democrats and a handful of Republicans were quick to condemn Trump's decision to fire Comey, who was investigating the Trump campaign's ties to Russia when he was unexpectedly fired Tuesday evening — one night after Trump used Twitter to condemn the "fake media" for reporting on the investigations into whether he colluded with Russia last year.

The dismissal has emboldened calls from both parties to the Justice Department, however, to appoint a special prosecutor to oversee the bureau's Russia's investigation. Others are insisting that Comey appear before the appropriate congressional committees to testify about the investigation now that he is a private citizen.

Republican Sen. Richard Burr, the chairman of the Senate Intelligence Committee, said he was "troubled by the timing and reasoning of Director Comey's termination." He added that Comey's firing "further confuses an already difficult investigation by the Committee" into Trump's Russia ties.

Democratic Sen. Mark Warner, the vice chairman of the Senate Intelligence Committee, said in a statement that Trump's "actions today make it clear to me that a special counsel must be appointed." He called Trump's decision "shocking" and "deeply disturbing" and argued that appointing a special counsel was "the only way the American people will be able to trust the results of any DOJ investigation."

Democratic Sen. Richard Blumenthal agreed: "The need for an independent special prosecutor is now crystal clear," he said.

FBI Director James Comey testifying in Washington on March 20 before the House Intelligence Committee hearing into alleged Russian meddling in the 2016 US election. REUTERS/Joshua Roberts

"Deputy Attorney General Rosenstein now has no choice but to appoint a special counsel," Democratic Sen. Patrick Leahy said in a statement. "His integrity, and the integrity of the entire Justice Department, are at stake."

Republican Sen. Ben Sasse, the chairman of the Senate Judiciary Committee's oversight subcommittee, called the timing of Comey's firing "very troubling."

"Regardless of how you think Director Comey handled the unprecedented complexities of the 2016 election cycle, the timing of this firing is very troubling," Sasse said in a statement.

"Jim Comey is an honorable public servant, and in the midst of a crisis of public trust that goes well beyond who you voted for in the presidential election, the loss of an honorable public servant is a loss for the nation ... I have reached out to the deputy attorney general for clarity on his rationale for recommending this action."

Others called for a select, bipartisan congressional commission to further the Trump-Russia investigation.

"I call on Speaker Paul Ryan to immediately appoint a bipartisan, non-classified, public and transparent commission to investigate the Trump-Russia relationship," Democratic Rep. Steve Cohen tweeted. "Our democracy is in danger."

Republican Sen. John McCain also weighed in: "I have long called for a special congressional committee to investigate Russia's interference in the 2016 election. The president's decision to remove the FBI director only confirms the need and the urgency of such a committee.”

Attorney General Jeff Sessions and Rod Rosenstein, the deputy attorney general, said in their statements that they recommended firing Comey because of how he handled the investigation into Hillary Clinton's email server. But New York Times reporter Michael Schmidt reported that Sessions had been trying to find an excuse to fire Comey for at least a week.

Attorney General Jeff Sessions arriving for a news conference Tuesday in Nogales, Arizona, after touring the US-Mexico border with border officials. Associated Press/Ross D. Franklin

Comey testified last week before the Senate Judiciary Committee, which oversees the FBI, about his handling of the investigations into Clinton and the Trump campaign. He reiterated that he felt he handled both appropriately but said it made him "mildly nauseous" to think his decision to revisit the Clinton email investigation on October 28 might have swayed the outcome of the election.

"At one extreme, the Trump White House might have been irked by Comey's testimony last week, particularly his discussion of the conduct of the Russian investigation and possibly his feeling ill that the FBI might have played some role in the November election," Deitz said.

"At the other extreme, it is possible that FBI interviews are being viewed with alarm in the White House, that is, that the circle appears to be closing," Deitz added. He said he doubted, however, that Comey's firing "will have any material effect on the Russia-Trump circle investigation."

"The FBI and DOJ are staffed with serious professionals who are impossible to intimidate," Deitz said. "If they feel that their investigation is being thwarted in any way, they will leak like hell to people like you."

Deitz referred to President Richard Nixon's "Saturday Night Massacre," in which he fired the independent special prosecutor, Archie Cox, who had been appointed by then-Attorney General Elliot Richardson to investigate the events surrounding the Watergate break-in. Nixon initially asked Richardson to dismiss Cox, but Richardson refused to do so and resigned in protest instead, along with then-Deputy Attorney General William Ruckelshaus.

In the Watergate scandal, Deitz said: "The firing of Archie Cox, Elliot Richardson, and William Ruckelshaus caused only a temporary blip in the investigation. In fact, it probably energized it."

Regardless of agents' leaking, however, whomever Trump appoints to lead the FBI will be able to halt the investigation at will. It will be up to Rosenstein — who recommended that Comey be fired — to appoint a special counsel to oversee the investigation. He has said he will not do that until he reviews all of the facts of the case and determines that it would be necessary.

Susan Hennessey, a former National Security Agency lawyer who is the editor-in-chief of the Lawfare blog, wrote Tuesday that she had "not previously called for a special prosecutor, believing that Rosenstein was a person of integrity who should be given a chance to make a call on that question."

"His performance today, however," she continued, "requires that he now step aside."

"He cannot credibly lead this investigation any longer," Hennessey added, "and leaders of both parties must make sure he steps aside for an independent prosecutor who can."