A renowned forensic biologist suspects Donald Trump suffers from narcissistic personality disorder which makes him "go nuclear" when he doesn't get his way or the praise he craves.
Dr Mark Benecke, who has analysed some of the world's worst killers and once examined Adolf and Eva Hitler's skulls, described the disgraced US president as a "crystalline narcissist" who would "rather die" than admit he lost the US election.
That type of person disguises their low self-esteem with charming behaviour, but will attempt to "destroy" anyone who doesn't give them the love or attention they desire, said Dr Benecke.
Narcissistic personality disorder can develop from "very, very low self-esteem" due to childhood neglect, emotional abuse or excessive pampering by parents, he added.
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Trump, 74, has been a president like no other with unprecedented fits of rage, bizarre and questionable decisions and unscripted outbursts, often on Twitter.
In addition to encouraging violence, he has courted white supremacists and far-right extremists, spread misinformation and conspiracy theories, and turned on allies while doing everything possible to cling to power and disparage his critics.
He may have cemented himself as the worst leader in US history when he incited a mob of his supporters to march on the Capitol on Wednesday, shortly before hundreds of them invaded the iconic building in one of the darkest days in America's history.
A police officer and four Trump fanatics died.
The violent scenes unfolded as lawmakers met to confirm President-elect Joe Biden's victory over Trump in November's election.
As the domestic terrorists occupied America's seat of power in a bid to overturn Trump's election defeat, he refused to condemn the insurrection and de-escalate the violence.
He later told the mob in a recorded message: "We love you. You're very special."
Dr Benecke told the Mirror: "He is a crystalline narcissist.
"I would not call him psychopathic because whether he is antisocial or not, that is another matter. Psychopaths are narcissistic and antisocial.
"Pure narcissistic personality disorder, that explains every detail of his behaviour.
"People with that disorder become aggressive and abusive, even more than before.
"They 'go nuclear' because the very core of their existence, their 'inner flame' is threatened.
"Trump did this all the time and it is very hard to understand why his staff did bear the strain. Probably self-abuse."
He pointed to the president's well-documented history of demeaning behaviour towards women as an example, saying "this is his 'normal' state of hate".
Dr Benecke said Trump "would rather die" than admit he lost November's presidential election.
Trump has falsely claimed the vote was rigged, and he continued to peddle his lies and paint himself as a victim even as he finally conceded on Thursday and condemned the deadly insurrection 24 hours too late.
One of the worst presidents ever will finally leave office as Biden and Vice President-elect Kamala Harris are sworn in on January 20, unless he is forced out before then.
It is likely that Trump will continue to make bogus claims and verbally attack Biden during his return to private life. There is speculation he could try to pardon himself before his time in the White House ends, and he could try run for president in 2024.
Dr Benecke predicted: "He will continue to harm and [insult] every person who stands in his way as hard, as often and as ugly as he can, except when he thinks the person might be useful.
"Then he will be friendly and charming to that person."
People with narcissistic personality disorder struggle to maintain relationships and care about no-one but themselves, the expert said.
He added: "Crystalline narcissism leads, not only in a politician, to a full, total, absolute disregard of the the interests of others except one single person - that one narcissist.
"This is not how a leader of people and their interests can function.
"The low self-esteem is often disguised by friendliness and charming behaviour because they love admiration, so they often seem to 'cooperate', but it's only to get attention.
"It is not true cooperation. They are just demanding energy, love, applause, praise.
"If that is not given unconditionally, the narcissist will try to 'destroy’ you, even if it is not necessary to reach his or her goals.
"They really think they are smarter, more beautiful, more intelligent, etc than anybody else.
"There is no cure and no treatment known since they do not see the problem. They see the therapist was an 'idiot' like everybody else."
Dr John Zinner, a leading psychoanalyst and clinical professor at the George Washington University School of Medicine, and other experts have also suggested Trump suffers from narcissistic personality disorder.
Trump's estranged niece, Dr Mary Trump, a clinical psychologist, recently wrote in her book, Too Much and Never Enough, that the president's father, Fred, was a high-functioning sociopath.
She suggested Donald Trump is a narcissist who may have severe mental health issues such as antisocial personality disorder, a learning disorder and dependent personality disorder, which make him unfit for office.
Dr Trump said her uncle struggles to control his impulses, learn new facts and tell the truth, among other things.
