U.S. President Donald Trump says he fired FBI Director James Comey for being a "showboat," acknowledging he had already made the decision when he asked his administration to come up with a rationale for the sacking – and that he was thinking about the FBI Russia investigation when he ousted him.

The President contradicted his own White House's story about the reasons for Mr. Comey's firing, only adding to the chaos consuming the Trump administration two days after Mr. Comey's removal as it scrambles to gain control of the narrative.

"Look: He's a showboat. He's a grandstander. The FBI has been in turmoil. You know that, I know that, everybody knows that. You take a look at the FBI, a year ago, it was in virtual turmoil, less than a year ago. It hasn't recovered from that," Mr. Trump told NBC's Lester Holt in an interview Thursday.

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Read more: Comey, Trump and the firing fallout: Five things to know

After the sudden firing Tuesday afternoon, the White House insisted Mr. Trump dismissed the head of the FBI after receiving a memo from deputy Attorney-General Rod Rosenstein that raised concerns with Mr. Comey's handling of the investigation last year into Hillary Clinton's e-mails.

Vice-president Mike Pence and deputy White House press secretary Sarah Huckabee Sanders both repeated this assertion Wednesday.

But Mr. Trump conceded Thursday it was not true.

In fact, he said, he was going to fire Mr. Comey no matter what Mr. Rosenstein concluded. And the Russia investigation was on his mind when he did.

"I was going to fire regardless of recommendation … and in fact, when I decided to just do it, I said to myself, I said 'You know, this Russia thing with Trump and Russia is a made-up story,'" he said.

Mr. Trump also said that at a White House dinner early in his term – at which Mr. Comey allegedly requested that he keep his job – the President asked Mr. Comey to confirm that Mr. Trump was not personally under investigation as part of the probe into the Trump campaign's ties to the Russian government.

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"We had a very nice dinner at the White House very early on … he wanted to stay on as the FBI head, and I said 'I'll consider, we'll see what happens,'" Mr. Trump told Mr. Holt. "I said 'If it's possible, will you let me know, am I under investigation?' He said 'You are not under investigation.'"

A somewhat different account of what appeared to be the same dinner emerged from Mr. Comey's camp. The New York Times, citing unnamed associates of the former director, said Mr. Trump twice pressed Mr. Comey at the Jan. 27 sit-down to promise the President his loyalty. Mr. Comey refused, telling him instead that he would be "honest."

Mr. Comey, the Times cited the sources as saying, was uncomfortable with agreeing to the President's invitation to the meal, and impressed upon Mr. Trump the importance of an independent FBI.

The President's decision to fire Mr. Comey comes as his Republican Party is trying to push through its legislative agenda, including a repeal of Obamacare and a coming package of tax reforms. So far, Mr. Trump has largely managed to keep his caucus behind him, even as Republican senators and House representatives have vowed to push forward with investigations of the Russia scandal. And on Thursday, the Senate invited Mr. Rosenstein to brief legislators on the firing.

But the sacking creates an enormous distraction, taking away any focus the GOP had on building support for its program.

"It makes it harder for the Republicans to move forward with their agenda because people have limited attention spans. This scandal, which is easier to understand than the health-care system or tax reform, is what people will focus on," said Gregory Wawro, a political-science professor at Columbia University.

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Meanwhile, at a Senate hearing Thursday, Mr. Comey's deputy directly contradicted the White House's assertion that Mr. Comey had lost the confidence of his own agency – one of the rationales the Trump administration had offered for throwing him out.

"No, sir, that is not accurate," said Andrew McCabe, who is now filling in as the agency's head. "I hold Director Comey in the absolute highest regard. I have the highest respect for his considerable abilities and his integrity … I can tell you, also, that Director Comey enjoyed broad support within the FBI and still does to this day."

Mr. Trump's willingness to contradict his own administration's account of Mr. Comey's firing pointed to profound disarray in the White House in the wake of what is perhaps the most consequential decision of the new administration. It also demonstrated that in moments of controversy, Mr. Trump believes that he is his administration's best spokesperson.

"His mode of operating is predictable unpredictability. This is an extension of what we've seen from him before, in his changing stories, but this is more explicit," said Prof. Wawro. "This is a very hamfisted way of doing what is often done in Washington: Make a decision, then come up with the reasons after. But to then admit that's what you're doing is, depending on what side of the divide you're on, either ludicrous or refreshingly honest."

Mr. Comey's renown wasn't always a source of tension. At a White House reception just days after his inauguration, Mr. Trump greeted Mr. Comey heartily with a handshake and a pat on the back and told onlookers, "He's become more famous than me."

Mr. Trump is "fascinated by stardom and celebrity," said Tim O'Brien, one of Mr. Trump's biographers, in an interview with The Globe and Mail late last year. "He's very aware of the power and the influence that goes along with it."

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Ultimately, Mr. Comey's problem may not have been his celebrity but his independence. "Everybody [Trump] has around him are people who have basically pledged loyalty to him," said a former federal prosecutor who knows Mr. Comey and who spoke on condition of anonymity. "If you haven't made that pledge of loyalty, you're not going to last."