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. View more opinion articles on CNN.

(CNN) You cannot go wrong by expecting the worst from Donald Trump.

Within 24 hours, he called on the attorney general to halt the investigation into his campaign's links to Russia, slammed the criminal prosecution of his former campaign manager Paul Manafort as a "hoax," and lied with great confidence at his Florida rally about his own popularity. Add his wacky claim that people need to present identification to buy groceries, and you get Trump at his worst.

Coming from any other President, Trump's brand of crazy talk -- much of it personal, ugly, and deranged -- would be enough to prompt calls for the White House doctor, who would, at the very least, prescribe some rest. But with Trump, statements that sound like he's trying to obstruct justice and distort reality no longer stir widespread outrage because he has taught the world to stop trying to make sense of what he says.

Eighteen months into his administration, Trump has bombarded us with so much awful noise that our minds have been trained to disregard much of it.

A good analogy from biology is what happens to people who work in foul environments and become desensitized to the odors. They just don't notice the stench anymore. In psychology, this process has been observed when it comes to violence. Repeated exposures inure people to the suffering.

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