WASHINGTON (WASHINGTON POST) - Former acting FBI director Andrew McCabe said in an interview that aired on Thursday (Feb 14) that he authorised an investigation into President Donald Trump's ties to Russia a day after meeting with him in May 2017 out of fear that he could soon be fired.

"I was very concerned that I was able to put the Russia case on absolutely solid ground in an indelible fashion that were I removed quickly or reassigned or fired that the case could not be closed or vanish in the night without a trace," McCabe told CBS.

His comments were the first time McCabe has publicly addressed why he opened an investigation into Trump following the firing of former FBI director James Comey, whose post McCabe took over.

CBS aired a portion of an interview scheduled to air in full on 60 Minutes on Sunday.

"I was speaking to the man who had just run for the presidency, and won the election for the presidency, and who might have done so with the aid of the government of Russia, our most formidable adversary on the world stage, and that was something that troubled me greatly," McCabe said, recalling his first meeting with Trump.

About two hours after the clip aired, Trump blasted McCabe on Twitter, calling him "a disgrace to the FBI and a disgrace to our Country."

"Disgraced FBI Acting Director Andrew McCabe pretends to be a 'poor little Angel' when in fact he was a big part of the Crooked Hillary Scandal & the Russia Hoax - a puppet for Leakin' James Comey," the president wrote, referring to an FBI investigation into Democrat Hillary Clinton's use of a personal e-mail while secretary of state in addition to its probe of possible coordination between the Trump campaign and Russia.

Trump said that McCabe "gave Hillary a pass."

In the clip that aired on CBS, McCabe did not address specific evidence that led him to believe Trump should be investigated personally.

It has been previously reported that the FBI began to explore at that point whether Trump was trying to obstruct justice, in part by firing Comey, and whether he personally was of concern from a counterintelligence perspective.

McCabe opened the case so quickly that some at the Justice Department were concerned that he might have acted too hastily because of Comey's removal, people familiar with the matter have said.

In a statement to CBS, White House press secretary Sarah Sanders said that McCabe had "opened a completely baseless investigation into the president."

In the interview, McCabe also apparently addresses allegations he made in memos documenting discussions with Deputy Attorney-General Rod Rosenstein.

It has been reported previously that McCabe alleged in the memos that Rosenstein suggested wearing a wire to surreptitiously record the president and that Cabinet members considered invoking the 25th Amendment to remove Trump from office.

During an appearance on CBS This Morning, Scott Pelley, the correspondent who interviewed McCabe, described the discussions of the 25th Amendment as "counting noses" - or speculating on where various Cabinet members might stand on the question.

Pelley said McCabe disputes the assertion, advanced by defenders of Rosenstein, that the deputy attorney-general was not serious about wearing a wire. Pelley said McCabe took the idea to FBI lawyers for a discussion afterward.

That, too, has been previously reported, though McCabe has never before publicly described his allegations.

A statement released by the Justice Department in response to the interview said that Rosenstein "again rejects Mr McCabe's recitation of events as inaccurate and factually incorrect."

"The Deputy Attorney-General never authorised any recording that Mr. McCabe references," the statement said. "As the Deputy Attorney-General previously has stated, based on his personal dealings with the President, there is no basis to invoke the 25th Amendment, nor was the DAG in a position to consider invoking the 25th Amendment."

McCabe sat for the interview as part of an effort to promote a new book, which is scheduled to be published next week.

As the interview clip aired, the Atlantic published an excerpt of McCabe's book, in which he describes his interactions with the president after Comey's firing.

In one encounter that he seems to view as particularly troubling, McCabe wrote that Trump pressed in an Oval Office meeting to visit the FBI, even though he had just fired its well-liked leader.

In McCabe's view, Trump was trying to enlist McCabe in a plan to send a sinister message to employees.

"In this moment, I felt the way I'd felt in 1998, in a case involving the Russian Mafia, when I sent a man I'll call Big Felix in to meet with a Mafia boss named Dimitri Gufield," McCabe wrote.

"The same kind of thing was happening here, in the Oval Office. Dimitri had wanted Felix to endorse his protection scheme. This is a dangerous business, and it's a bad neighbourhood, and you know, if you want, I can protect you from that. If you want my protection. I can protect you. Do you want my protection?

"The president and his men were trying to work me the way a criminal brigade would operate."

A frequent punching bag for President Trump, McCabe was fired from the bureau in March just 26 hours before he could retire, after the inspector-general presented Justice Department leadership with allegations that McCabe had authorised a disclosure to the media and then lied repeatedly to investigators about it.

The timing of the firing cost McCabe a significant portion of his retirement benefits.

In his tweet on Thursday, Trump characterised the inspector-general report as "devastating."

McCabe alleged his termination was politically motivated and meant to discredit the bureau and the ongoing Russia probe.