Michael D'Antonio is the author of the book " Never Enough: Donald Trump and the Pursuit of Success " (St. Martin's Press). This article is adapted in part from a CNN Opinion piece originally published in 2016. The opinions expressed in this commentary are those of the author.

(CNN) With only weak and belated denials, the world is left to ponder the reports that President Trump described some African nations as "shithole countries" while protesting the idea of admitting immigrants from, let's face it, countries where people are generally black and brown.

Trump also said he'd prefer more people from Norway, where the population is as white as it gets. (Sen. Dick Durbin, present at the meeting, contested Trump's denial, saying, "He said these hate-filled things. And he said them repeatedly.")

If you think the President hasn't exhausted the benefit of the doubt he deserves when it comes to racism, consider how he said there were "some very fine people" among the white separatists and neo-Nazis who recently rallied in Charlottesville. Earlier this year, according to The New York Times, he also complained that Haitians "all have AIDS."

Trump has shown us a habit of mind that sees admirable folks among white nationalists and lots of negative things to say about non-whites. This isn't dog whistle bigotry, it is megaphone prejudice sounded by the highest official in the land. It is also a brand of politics that Trump has practiced -- divide, exploit, repeat -- for a considerable time.

It is the pattern, and White House officials' silence on the "shithole" comment, that leads us to discount the President's claim that this was not the language he used.

With backing from diehard supporters, Trump urged us to be outraged instead by the "outlandish proposal" made by lawmakers who visited him to discuss immigration. This rhetoric shouldn't deflect our attention from the fact that Trump has so debased his office that we are reduced to repeating his gutter language in order to address his unacceptable behavior.

Many of us readily believe the reports of Trump's comment because we know him to be notoriously crude. For years he has displayed an obsession with race, ethnicity, religion and gender. When he was merely a bragging businessman, his relentless effort to alienate us from each other could be dismissed as a private citizen's character flaw -- of less consequence because he was essentially a showman and a hype artist.

When he stepped into the national political arena, and continued this kind of talk, he became a more dangerously divisive figure who threatened the norms that make America the agreeable, noisy, diverse, and creative country the world admires.

During the presidential campaign, Trump told the Wall Street Journal that Gonzalo Curiel, the federal judge hearing the fraud complaints against his defunct Trump "University" should disqualify himself because he is of Mexican descent. "I'm building a wall," said Trump, referring to his call for a huge border wall between the US and Mexico, so the judge has "an inherent conflict of interest."

Trump defended the comments in an interview with CNN's Jake Tapper, saying: "He's proud of his heritage. I respect him for that," yet adding, "He's a Mexican." In fact, the judge was born in the United States.

It is, of course, only human for us to feel anxiety about people who may be different from us. The tendency to categorize others is a well-established element of human nature. But it is also human to seek to work against our prejudices and to understand that others always deserve respect.

Swedish, not German?

For at least four decades, Trump has aired rather strange views about heritage and identity. As a young man, he repeated his father Fred's false claim that the Trump family -- the name was once Drumpf -- emigrated from Sweden, and not Germany. The senior Trump began calling himself Swedish after World War II because, as Donald Trump told me, he didn't want Jewish New Yorkers to connect him with the Nazi regime and take their business elsewhere.

This assumption, which Donald agreed with, betrays an exceedingly dim view of human nature. The Trumps expected bigotry from Jewish New Yorkers and they were willing to turn their backs on their ancestors to make money.

As Donald Trump moved through his adult life, he has regularly demonstrated an extraordinary level of concern about the ethnic and racial identity of people he encountered. When he testified before a committee in Congress about competing casino operators from Native American tribes, he complained, out loud, that they "don't look like Indians to me."

In his book about Trump's years as a casino operator in Atlantic City, former Trump executive John R. O'Donnell wrote of how his boss made bigoted statements about African-Americans and Jews. O'Donnell quoted Trump saying:

"Black guys counting my money! I hate it. The only kind of people I want counting my money are short guys wearing yarmulkes... Those are the only kind of people I want counting my money. Nobody else ... Besides that, I tell you something else. I think that's guy's lazy. And it's probably not his fault because laziness is a trait in blacks."

Trump has both confirmed and denied the accuracy of O'Donnell's reporting. In May 1997, he told Playboy writer Mark Bowden about the book generally, "The stuff O'Donnell wrote about me is probably true." Two years later, when he was eying a third-party run for president he told Tim Russert, "I've never said anything like it."

Fair housing case

Prior to Trump's involvement in gambling, his real estate organization was subject to a crackdown by the US government for failing to comply with fair housing laws governing applications for apartments by minorities. Trump answered with a countersuit in which his lawyer likened the feds to the "Gestapo" and "storm troopers."

The countersuit was dismissed by the judge in the case. In the end, Trump settled the case by agreeing to comply with the law and without admitting wrongdoing.

In 1989, he was back in the press again, telling Bryant Gumbel that, "A well-educated black has a tremendous advantage over a well-educated white in terms of the job market."

Foreigners have also come in for Trump's prejudice on a regular basis. In the 1980s it was the Japanese who secretly "laugh like hell" after completing unfair business deals. Now it's the Chinese, whom Trump mocks by speaking broken English, but also offers as the wily, if not sneaky, bargainers who take advantage of America.

Leader of the birthers

For much of President Obama's presidency, Trump led the so-called "birther" movement, alleging, in ridiculous defiance of all evidence, that Obama was born outside the US and may not be a real American citizen. This campaign, which he pursued long after others dropped it, was clearly an attempt to turn the first African-American president into a foreign "other" and thus, presumably, render him illegitimate.

When comedian Jon Stewart went after him on his satirical nightly broadcast, Trump reached once again for an argument based on ethnicity. He tweeted: "If Jon Stewart is so above it all & legit, why did he change his name from Jonathan Leibowitz. He should be proud of his heritage!" This from a German-American man who had posed as Swedish.

Trump started off his run for the presidency with a bigoted rant about undocumented Mexicans, braying about how "they're bringing drugs, they're bringing crime. They're rapists." The effect of this talk was to ramp up public anxieties about people who are actually less likely to commit crimes than others. A pair of Massachusetts men were arrested for beating a Latino person they encountered on the street and, according to police, one of them said, "Donald Trump was right."

Next, Trump retweeted false "data" alleging that black assailants account for more than 80% of white deaths due to homicide. The numbers were too high by a factor of five.

And don't forget Donald Trump's attitudes about the 1.5 billion Muslims of this world. One of his first acts as president was to establish a travel ban, which has since been modified, that targeted citizens of seven Muslim-majority countries.

Dividing Americans

Trump's divisive view of people is a deeply felt belief that he has passed on to the younger generation of Trumps. His eldest son Donald Jr. told me that, "Like him [Donald Sr.], I'm a big believer in race-horse theory. He's an incredibly accomplished guy, my mother's incredibly accomplished, she's an Olympian, so I'd like to believe genetically I'm predisposed to better-than-average."

In Trump's world, comments about a person's ethnic and racial background are fair game. And yet he says , "I am the least racist person you have ever met."

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Trump's kind of thinking was common in the 1950s, when he was a boy. This is the period evoked when he says he wants to "Make America Great Again." In fact, the 1950s were marred in many ways, including by the stereotypes people clung to about group identity.

Thankfully, most Americans grew beyond this type of thinking and learned to consider people as individuals and view character as paramount. What's most worrying about Trump is the evidence that he has not joined the rest of us.