Donald Trump "lies constantly" and is "morally unfit" to be US President, according to former FBI boss James Comey.

The man fired by Mr Trump last year told ABC News: "I don't buy this stuff about him being mentally incompetent or early stages of dementia.

"I don't think he's medically unfit to be President. I think he's morally unfit to be President," he added.

Lashing out in a series of tweets before the interview was aired, the President described Mr Comey as a "slimeball" and the "WORST FBI director in history, by far".

He said Mr Comey was lying and is "not smart".


Comey drafted the Crooked Hillary exoneration long before he talked to her (lied in Congress to Senator G), then based his decisions on her poll numbers. Disgruntled, he, McCabe, and the others, committed many crimes! — Donald J. Trump (@realDonaldTrump) 16 April 2018

After the interview was aired, Mr Trump hit back in another tweet, accusing Mr Comey of committing "many crimes".

"Comey drafted the Crooked Hillary exoneration long before he talked to her (lied in Congress to Senator G), then based his decisions on her poll numbers," he tweeted.

"Disgruntled, he, McCabe, and the others, committed many crimes!"

The former FBI chief appeared to hold nothing back when he got in front of the cameras.

Slippery James Comey, a man who always ends up badly and out of whack (he is not smart!), will go down as the WORST FBI Director in history, by far! — Donald J. Trump (@realDonaldTrump) April 15, 2018

I never asked Comey for Personal Loyalty. I hardly even knew this guy. Just another of his many lies. His “memos” are self serving and FAKE! — Donald J. Trump (@realDonaldTrump) April 15, 2018

"[He] talks about and treats women like they're pieces of meat [and] lies constantly about matters big and small," said Mr Comey.

He also said it was "stunning" to think that Russia could have compromising information on the President, but that he could not discount the possibility.

Mr Comey has kept quiet about his time under Mr Trump for nearly a year, with the interview and his new tell-all book, A Higher Loyalty, breaking the silence.

The former lawyer also compared the President to one of the mafia bosses he once took on, calling his leadership "ego driven and about personal loyalty".

He told ABC that Mr Trump had told him "I expect loyalty, I need loyalty" during an awkward dinner at the White House.

The President rubbished the claim on Twitter, calling it "another of his many lies".

Mr Comey also said there was possibly "some evidence of obstruction of justice" in another of his claims - that Mr Trump had asked him to "let go" a criminal investigation into the President's former national security adviser, Michael Flynn.

Image: Donald Trump denies asking James Comey for his personal loyalty

Mr Comey was sacked in May 2017, with officials accusing him of mishandling the investigation into Hillary Clinton's use of a personal email address.

Many Democrats blame his decision to reopen the probe - just 11 days before the 2016 election - for Mrs Clinton's defeat.

In the interview, Mr Comey said he assumed Mrs Clinton would win.

He told ABC: "I don't remember spelling it out, but it had to have been, that she's going to be elected president and if I hide this from the American people, she'll be illegitimate the moment she's elected, the moment this comes out."

Opponents have suggested Mr Comey was dismissed because he was leading the investigation into alleged links between Mr Trump's campaign team and Russia.

Mr Trump's letter firing Mr Comey said he was losing his job on the recommendation of the Attorney General.

Another former FBI director, Robert Mueller, is now in charge of the ongoing Russia-Trump investigation.

His remit now also includes whether the President obstructed justice when he fired Mr Comey.