The co-author of Donald Trump’s memoir The Art of the Deal has said the US President harbours a deep-seated desire to become a dictator.

Tony Schwartz, who claims he ghost-wrote the 1987 best-selling business book, said the prospect of war actively excites President Trump and he lacks the emotional intelligence needed to comprehend the devastating consequences of conflict.

Schwartz, who spent 18 months interviewing and shadowing Mr Trump back in the 1980’s, claimed the world leader had the characteristics of a sociopath and the prospect of millions of death did not rouse normal feelings of guilt.

Schwartz’s comments come after US lawmakers raised concerns over President Trump’s control of the nuclear arsenal. Senators debated revoking the US president’s decades-old power to unilaterally mount a first strike at a hearing on Tuesday.

Senator Chris Murphy said: “We are concerned that the President of the United States is so unstable, is so volatile, has a decision-making process that is so quixotic that he might order a nuclear weapons strike that is wildly out of step with US national security interests”.

Growing concerns are prompted by President Trump partaking in an escalating war of words with Kim Jong-Un and exchanging personal insults and threats of military strikes with the North Korean leader. In August, President Trump claimed he would meet North Korea with “fire and fury like the world has never seen”. In October, Mr Trump threated to “totally destroy” the country in a pugnacious speech to the UN.

Schwartz, who has been an outspoken critic of the US president, argued that the prospect of World War III enlivened the president.

“I actually think it’s that it kind of excites him. That’s a horrible thing to have to think but domination is his thing,” he said during an appearance on The Last Word on MSNBC. 

“As far back as 15 months ago, I said to the New Yorker that I was deeply concerned that if he got elected he would potentially get irritated by Kim Jong-Un and set off the nuclear codes or punch him in. People laughed and said what are you talking about. Now it’s a very, very real possibility.”

He added: “It’s very evident that he deeply would like to be a dictator and the idea that Senator Ben Cardin says people haven’t interpreted it means he is considering a nuclear war. No, he has said it six ways from Sunday that is the case”.

Mr Schwartz has previously talked about how well he got to know Mr Trump while working on The Art of the Deal, saying he spent hundreds of hours talking to him about his life, listening to him, and generally observing him in the flesh.

Schwartz, who said he would rename The Art of the Deal as The Sociopath if he could, argued President Trump’s lack of empathy could put the world in grave danger.

“A sociopath is someone who doesn’t have a consciousness who doesn’t have ordinary emotions beyond anger, rage and so on,” he said during his latest appearance. “The idea of destroying an entire country and millions of people doesn’t fire up his sense of guilt and feeling of being appalled.” 

“Again I think he finds that kind of exciting. It’s some blend of a very young child’s idea of fighting with guns or nuclear weapons and a very demented older person potentially putting us at great pale.”

He added: “Trump always explains thing between win and lose. Why win and lose? Because lose is the equivalent of death and if you’re going to be faced with death you are going to choose.”

Schwartz contributed to The Dangerous Case of Donald Trump, a book published last month which sees 27 psychologists, psychiatrists, and mental health professionals join forces to assess President Trump’s mental health based on his speech and behaviour throughout his lengthy period of time in the public sphere. The book reaches the conclusion the billionaire property tycoon poses a serious danger to not just America but the whole world. 

“Beneath his bluff exterior, I always sensed a hurt, incredibly vulnerable little boy who just wanted to be loved,” writes Schwartz in the book.

Schwartz has been a steadfastly vociferous critic of Mr Trump since he announced his presidential bid. Last year he revealed he was advising the campaign of Mr Trump’s Democrat rival Hillary Clinton for free as “penance” for boosting the US president’s profile by ghostwriting his book and helping him forge his reputation as a savvy businessman.

He has also expressed great regret about the positive slant he put on President Trump in the book, saying the glowing representation was akin to himself having “put lipstick on a pig”.

“My second greatest fear about Trump (after launching nuclear weapons): his amazing ability to normalise horrific behaviours by repeating them so often that people eventually go numb. Scares the bejesus out of me,” Schwartz wrote on Twitter on Tuesday.

There have been some disputes between Mr Schwartz and Mr Trump about who wrote the book. The president has challenged Mr Schwartz’ position as the ghostwriter via his legal team but Mr Schwartz claims he has proof from his publisher Random House that he wrote the entire book.

Mr Schwartz, who shared credit as a co-author with Mr Trump, claims Mr Trump only did some minor editing of the book which he peddled during his campaign as evidence of his skills as a negotiator. President Trump has acknowledged Mr Schwartz as his co-author but insisted he wrote his own memoir, saying: “He owes a lot to me. I helped him when he didn’t have two cents in his pocket. It’s great disloyalty. I guess he thinks it’s good for him – but he’ll find out it’s not good for him.”