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President Trump made clear early Saturday that he viewed Attorney General Jeff Sessions' decision to fire former FBI Deputy Director Andrew McCabe as a “great day for Democracy.”

“Andrew McCabe FIRED, a great day for the hardworking men and women of the FBI — a great day for Democracy!” Trump wrote on Twitter, before deriding former FBI Director James Comey, who Trump fired in May 2017.

Andrew McCabe FIRED, a great day for the hard working men and women of the FBI - A great day for Democracy. Sanctimonious James Comey was his boss and made McCabe look like a choirboy. He knew all about the lies and corruption going on at the highest levels of the FBI! — Donald J. Trump (@realDonaldTrump) March 17, 2018

Trump's ire did not stop there. After reports on Saturday night revealed that McCabe kept notes of his meetings with Trump, the president dismissed the claim on Twitter and took another shot at Comey.

Spent very little time with Andrew McCabe, but he never took notes when he was with me. I don’t believe he made memos except to help his own agenda, probably at a later date. Same with lying James Comey. Can we call them Fake Memos? — Donald J. Trump (@realDonaldTrump) March 18, 2018

Comey responded to Trump's earlier allegations via a tweet on Saturday night, saying he would soon share his story and the public "can judge for themselves who is honorable and who is not."

The former FBI director has a forthcoming book called "A Higher Loyalty: Truth, Lies, and Leadership." Set for release on April 17, the book on Sunday had was No. 1 on Amazon's best sellers list based on pre-orders.

A source familiar with the situation told NBC News Saturday that McCabe kept notes of his interactions with Trump, and they were turned over to special counsel Robert Mueller’s team some time ago. The news that Mueller had the notes was first reported by The Wall Street Journal.

Mueller is investigating Russian interference in the election and whether there was any coordination with those connected to the Trump campaign, as well as possible obstruction of justice by Trump associates.

Trump on Sunday reiterated his frequent refrain that there was "no collusion" between Russia and the Trump campaign. He insinuated instead on Twitter Saturday that there was leaking and corruption "at the highest levels of the FBI, Justice & State."

Sessions accepted the agency’s recommendation to fire McCabe late Friday — two days before the veteran FBI official planned to retire and become eligible for full pension and benefits.

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Related: Sessions fires McCabe before he can retire

The FBI's Office of Professional Responsibility proposed McCabe’s termination after the Justice Department's inspector general concluded McCabe had made “unauthorized disclosure to the news media and lacked candor — including under oath — on multiple occasions.”

But in a statement Friday, McCabe, who has spent two decades at the FBI, said he viewed his firing as a partisan decision that is part of the Trump administration’s “ongoing war on the FBI and the efforts of the Special Counsel investigation.”

Related: McCabe: Trump wants to destroy me to stop Mueller probe

The firing and Trump's response sparked outrage from Republicans, Democrats and former members of the intelligence community who have cast the decision to remove McCabe as something akin to a political hit-job.

Sen. Jeff Flake, R-Ariz., told Jake Tapper on CNN's "State of the Union" that McCabe's firing was a "horrible day for democracy" and called a White House offensive against the special prosecutor a "red line."

"I just hope that enough people would prevail on the president now," Flake said. "Don’t go there, don’t go there we have confidence in Mueller. I certainly do."

Sen. Lindsey Graham, R-S.C., added on "State of the Union" that the Senate Judiciary Committee should hold a hearing on the matter of McCabe's firing.

"I think we owe it to the average American to have a hearing in the Judiciary Committee where Mr. Sessions, Attorney General Sessions, comes forward with whatever documentation he has about the firing, and give Mr. McCabe a chance to defend himself," Graham said.

Sen. Angus King, I-Maine, speaking to CBS "Face the Nation" moderator Margaret Brennan, said the firing of McCabe appeared to be an act of "vengeance."

But the reactions first came in on Saturday when John Brennan, the former director of the CIA slammed what he described as Trump's “venality, moral turpitude, and political corruption.”

When the full extent of your venality, moral turpitude, and political corruption becomes known, you will take your rightful place as a disgraced demagogue in the dustbin of history. You may scapegoat Andy McCabe, but you will not destroy America...America will triumph over you. https://t.co/uKppoDbduj — John O. Brennan (@JohnBrennan) March 17, 2018

Sen. Patrick Leahy, D-Vt., who serves on the Judiciary Committee, requested Republican Chairman Chuck Grassley hold an urgent hearing on the politicization of the Justice Department.

In a statement, Leahy said he'd never witnessed anything like the current political attacks against career Justice Department officials in his four decades on Capitol Hill.

"What we are seeing today is dangerous, and demands our immediate attention," Leahy wrote. "I believe the Judiciary Committee will fail to fulfill its core oversight responsibility if it does nothing in this moment."

Related: Trump's attorney John Dowd calls for end to Mueller probe, cites firing of McCabe

Lawmakers on both sides of the aisle called for the swift release of the inspector general’s report so that the public could judge the merits of McCabe’s removal.

Adam Schiff, D-Calif., a ranking member on the House Intelligence Committee, said the absence of the IG's report makes McCabe's removal appeared overtly political.

“That it comes after the president urged the DOJ to deprive McCabe of his pension, and after his testimony, gives the action an odious taint,” Schiff tweeted.

But some Republicans defended McCabe's firing on Sunday.

On CBS' "Face the Nation," Sen. Rand Paul, R-Ky., called McCabe's termination "appropriate" if the inspector general's conclusions are correct. He also added that the "FBI needs to learn to stay out of politics."