President Trump's firing of FBI Director James Comey in the middle of several investigations of possible Trump campaign ties to last year’s Russian meddling in U.S. elections caused a firestorm of protest from Democratic members of Congress, with many calling for the appointment of a special prosecutor.

Some equated the firing with events known as the "Saturday Night Massacre" during the Watergate scandal that brought down President Richard Nixon.

Senate Minority Leader Charles Schumer, D-N.Y., said he told Trump that he had made a “big mistake” when informed of the decision.

Schumer wondered aloud whether the firing meant Comey’s investigation was “getting too close to home,” and he said the handling of a credible investigation depends on Deputy Attorney General Rod J. Rosenstein naming a “fearless, independent” special prosecutor.

“Mr. Rosenstein, America depends on you to restore faith in our criminal justice system which is going to be badly shattered after the administration’s actions today," Schumer said.

Republican Sen. John McCain of Arizona called for the creation of a special congressional committee on Russia, while Republican Rep. Justin Amash of Michigan said he and his staff were "reviewing legislation to establish an independent commission on Russia."

"James Comey is a man of honor and integrity, and he has led the FBI well in extraordinary circumstances," McCain said.

Comey, a Republican who had served in the George W. Bush administration as second in command in the Justice Department, was the surprise choice of President Barack Obama for the FBI post.

He had established his independence in March 2004 when then-White House counsel Alberto Gonzales sought to get Comey’s boss, Attorney General John Ashcroft, to sign off on a secret National Security Agency wiretap program. Ashcroft, seriously ill in the hospital with pancreatitis, had turned his duties over to Comey, who told Gonzales in Ashcroft’s hospital room that he refused to authorize the program.

Rep. Adam Schiff of California, the top Democrat on the troubled House intelligence committee, said the firing raised profound questions about White House interference in a criminal probe.

“The decision by a president whose campaign associates are under investigation by the FBI for collusion with Russia to fire the man overseeing that investigation, upon the recommendation of an Attorney General who has recused himself from that investigation, raises profound questions about whether the White House is brazenly interfering in a criminal matter,” Schiff said, likening the event to the Watergate firings.

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Senate Minority Whip Dick Durbin, D-Ill., suggested Trump’s action poses serious constitutional issues, while others called the development “Nixonian.”

“The termination and removal of James Comey as director of the Federal Bureau of Investigation raises the critical question as to whether the FBI investigation of Russian interference in the last presidential campaign will continue,” Durbin said.

Sen. Ron Wyden, D-Ore., a member of the Senate committee probing the Trump-Russia connection, called the firing “outrageous.”

“I have been long been a critic of Director Comey ... but Donald Trump’s decision to fire him now, in the midst of an investigation into Trump associates and their ties to Russia, is outrageous," Wyden said. He said Comey should be called to testify before Congress about the status of the Trump-Russia investigation.

“The president would do well to remember that in America, the truth always comes out.”

Sen. Patrick Leahy, D-Vt., who questioned Comey at a hearing before a Judiciary subcommittee this week, said the way Trump is handling the firing “is shocking.”

“No one should accept President Trump’s absurd justification that he is now concerned that FBI Director Comey treated Secretary Clinton unfairly,” Leahy said. “The president has removed the sitting FBI Director in the midst of one of the most critical national security investigations in the history of our country. This is nothing less than Nixonian.”

Leahy also noted that Attorney General Jeff Sessions, whom the president consulted before the firing, was supposed to have recused himself. He said Rosenstein now has no choice but to appoint a special counsel.

A long list of others calling for an independent probe included Sens. Richard Blumenthal, D-Conn., Ben Cardin, D-Md., Cory Booker, D-N.J., Kamala Harris, D-Calif., Joe Donnelly, D-Ind., and Bill Nelson, D-Fla., along with good government advocacy groups MoveOn.org and Common Cause.

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Others reacted with more measured tones. Sen. Dianne Feinstein, D-Calif., the ranking member of the Judiciary Committee, said simply that she had been informed by the president of his decision by phone, adding, “the next FBI director must be strong and independent and will receive a fair hearing in the Judiciary Committee.”

One of the earliest Republican reactions came from Foreign Relations Chairman Bob Corker, R-Tenn.: “While the case for removal of (FBI Director Comey) laid out by Deputy Attorney General Rod J. Rosenstein was thorough, his removal at this particular time will raise questions."

News of Comey’s departure came near the end of an hourlong telephone town hall meeting that House Appropriations Chairman Rodney Frelinghuysen, R-N.J., was having with constituents. “Lisa in Mendham” said she wanted to know what Congress was going to do now to hold Trump accountable “for his potentially breaking the law in dealing with Russia.”

Frelinghuysen didn’t answer that question directly but gave a positive appraisal of the job Comey has done.

“He had the reputation ... like his predecessor Robert Muller, of being a sort of straight-arrow guy,” Frelinghuysen said. “I do think he was an honorable man and represented an amazing department. I'm surprised he's gone. But in this business, I guess nothing is too surprising.”

Reporters Herb Jackson and Eliza Collins contributed to this story.