THE man who co-wrote Donald Trump's best selling book The Art of the Deal has claimed if he is elected president he will impose martial law.

Tony Schwartz has blasted the Republican nominee claiming he will behave in a way that make Richard Nixon's actions look like "child's play".

7 Schwartz said: "I started out saying … that my highest fear was that because he was so thin-skinned, and because he is so insecure, he is a huge risk to set off, to punch in, the nuclear codes, because he happens to be irritated or frustrated by an enemy." Credit: Getty Images

Speaking to The Independent the writer said: “I started out saying … that my highest fear was that because he was so thin-skinned, and because he is so insecure, he is a huge risk to set off, to punch in, the nuclear codes, because he happens to be irritated or frustrated by an enemy.

“When I said that, I got a lot of rolling of the eyes from people in the media and other people to whom I was making that case.

"I think today, people do really begin to understand that this is a volatile man with very low self control.”

7 Donald Trump has in the past dismissed Schwartz's criticisms Credit: Getty Images

Schwartz first broke his silence in July when he branded The Donald a "sociopath" and a "liar".

In an interview with the The New Yorker he said: “I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilisation.”

Of the book he said: “I put lipstick on a pig. I feel a deep sense of remorse that I contributed to presenting Trump in a way that brought him wider attention and made him more appealing than he is.”

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Schwartz appeared on ABC on Monday in the US, and said he had been having sleepless nights since Trump entered the race for the White House.

He told ABC: “You know, it's a terrifying thing, I haven't slept a night through since Donald Trump announced for President because I believe he is so insecure, so easily provoked and not particularly-- nearly as smart as people might imagine he is.

7 Tony Schwartz, who was hired by the Republican presumptive candidate to co-write the business guide, branded him a “sociopath” and said "he would lie about anything" Credit: abc

“And in the face of somebody like Putin provoking him cleverly - because Putin's a whole heck of a lot smarter than Donald Trump - I do worry that with the nuclear codes he would end civilization as we know it.”

Schwartz and Trump met in 1985 – he interview him for an article which appeared in New York magazine, and despite it being critical of the business mogul, he said he liked it.

7 Schwartz appeared on ABC on Monday in the US, and said he had been having sleepless nights since Trump entered the race for the White House Credit: abc

In the New Yorker article he explained: “Trump only takes two positions. Either you’re a scummy loser, liar, whatever, or you’re the greatest. I became the greatest. He wanted to be seen as a tough guy, and he loved being on the cover.”

7 He said he regretted being involved in the book

It was when he did a second interview for Playboy Trump offered the option of ghostwriting the book.

Schwartz said yes as long as he got half of the $500,000 in advance, 50 per cent of the royalties and was named as co-author.

The pair started work on the book in 1986 and it was not easy – the author said it was difficult to get Trump to recall his childhood, and Trump found it hard to focus, saying: “it’s impossible to keep him focused on any topic, other than his own self-aggrandizement, for more than a few minutes.”

7 Trump denied Schwartz's claims Credit: abc

He added: “If he had to be briefed on a crisis in the Situation Room, it’s impossible to imagine him paying attention over a long period of time.”

In a bid to hear Trump talk, he began to listen into his phone calls, and it was then he says he heard him lying: “Lying is second nature to him.

7 The Art of the Deal was a best seller in the late 1980s Credit: abc

"More than anyone else I have ever met, Trump has the ability to convince himself that whatever he is saying at any given moment is true, or sort of true, or at least ought to be true.”

One of the alleged lies which was told was in relation to a false claim that Prince Charles had been interested in buying an apartment in Trump Tower.

Schwartz said: “He lied strategically. He had a complete lack of conscience about it,' Schwartz said, something that 'gave him a strange advantage' over people who were 'constrained by the truth.”

In relation to the opening lines of the book: “I don't do it for the money ... I do it to do it ... That's how I get my kicks”, which Schwartz says he wrote in Trumps voice, the writer said: “Of course he’s in it for the money. One of the most deep and basic needs he has is to prove that ‘I’m richer than you.’”

He told ABC that he had kept quiet about the book until now because the pair had had a successful experience together and Schwartz never thought Trump would have been going for the White House: “I never in a million years thought he would have run for president.

“If I had through that 30 years ago I wouldn't have written the book. But for 29 years I didn't think he would and it didn't seem like it was important to speak out. I now feel it's my civic duty.”

He added: 'I this is a man who has more sociopaths tendencies than any candidate in my adult life that I've observed and so, yeah, I do regret writing the book.”