Michael D'Antonio is author of the book, "Never Enough: Donald Trump and the Pursuit of Success " (St. Martin's Press). The opinions expressed in this commentary are his.

(CNN) In the end it took innocent children -- or, as Time magazine depicts it , a single little girl -- to reveal the true Donald Trump to those who have resisted recognizing him. In the magazine's cover illustration, this tiny toddler stands in her pink sneakers, her sobbing face turned upward. Looking down, from his impassive height, Trump gazes as if at an insect or inanimate object. This is a man who can use the word " infest " as he regards fellow human beings.

Trump's reign of cruelty reached a sadistic crescendo this week as we learned that his administration had ordered more than 2,300 children, including nursing infants, torn from their parents and locked up. Their offense? Accompanying parents who claim refugee status as they cross America's southern border.

Those who were shocked to hear audio of wailing toddlers and see images of family separations haven't been paying close attention. Whether you consider the Polish workers treated like beasts of burden at his Trump Tower building site in 1980 or his nasty public divorce from his first wife, Ivana, in the early 1990s, Donald Trump has repeatedly demonstrated that he is willing to sacrifice others for his own benefit and that he feels no shame about anything. Only a man with amoral instincts would mock a reporter's disability, as Trump did during his campaign. Only a supremely narcissistic leader would turn on essential allies and embrace despots, as Trump has, with so little regard for his country's moral standing.

Just last night Trump dismissively referred to his sometime opponent Senator John McCain, castigating him for his vote against repealing Obamacare. "We had a gentlemen, way into the morning hours, go thumbs down," Trump said, without naming the senator, who is stricken with cancer. "He went thumbs down." One member of the audience shouted , "He's a war hero! He's a war hero!"

A day earlier the President maintained his all-about-me focus when he met with Congressional Republicans to discuss the family separation scandal. In true bully fashion, he asked about the whereabouts of his antagonist, Rep. Mark Sanford of South Carolina. He was tweaking Sanford over his defeat in a recent primary. The quip was met with groans, as fellow Republicans couldn't stomach it . "That's kind of kicking a man when he's down," a member of House who was in the meeting told CNN. "That's not who we are."

How is it that Trump carries on in this way, despite the disgrace and the rejection? As someone who has studied him for years, and spent ample time with Trump and his family, I keep coming back to the man's malformed character. Something in Trump's experience, or perhaps biology, interrupted the developmental process that creates in us the ability to care about others. In Trump's heart resides only himself. There is no room for a crying child.

The President understands that key elements of a person's personality are established early in life. Thus, the most chilling thing Donald Trump ever told me was that he believes that by age six he was the person he would always be. I thought of the fact that at age six he was a bully, whose status, as the son of one of the most powerful men in New York, made his deviance worse. In his book "The Art of the Deal," Trump confessed that in second grade he gave a teacher a black eye. By the time he was thirteen he was so obviously out of control that his parents sent him off to military school for discipline.

Trump's mean streak, amplified by his money, allowed him to exploit others in love and business and, eventually, politics. As a candidate, his method thrilled many voters, who themselves responded like children in a bully's thrall, and as President he has attracted like-minded people to his service. Who but a bully's enabler would, as Homeland Security chief Kirstjen Nielsen did, insist that family separation wasn't Trump policy? Who but a like-minded bully like White House adviser Stephen Miller would describe the choice of separating families as a "simple decision."

The world is amply supplied with people like Miller, who seem to take pleasure in suffering. Consider Corey Lewandowski , Trump's former campaign manager now working to boost Vice President Mike Pence, who mocked the case of a ten-year-old disabled girl separated from her mother at the border -- or Pence himself, who professes Christian faith but stands by as children suffer.

Those who had defended the administration's handling of the immigration issue, like Pence, Lewandowski, Nielsen and others were in an uncomfortable position when Trump suddenly stopped the separation policy. (It's notable that there is no well thought-out plan for reuniting kids and parents already torn apart.) The fact that the President could pull the rug out from under these loyalists comes as no surprise. No amount of service is enough to win fair and equitable treatment from Donald Trump. Just ask former Trump campaign chairman Paul Manafort, now in jail awaiting trial. The President now talks about him as if he barely knew him.

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Manafort's experience proves that everything Trump does with fellow human beings is a transaction and that he expects every exchange to benefit him. It is proof that Republicans in Congress should consider, as they weigh working with a man whose ruthlessness knows no bounds. As the mental health experts who contact me daily say, this 72-year-old boy bully is only going to get worse. And the only choice for those who fear for their country, as well as the children, is to stand against him.