Washington — Historians studying the Trump presidency will have a prodigious amount of digital material that demands examination but defies explanation. The president’s Aug. 21 half-hour South Lawn press availability deserves to be at the top of that list.

With the whir of a helicopter engine in the background, Donald Trump veered from topic to topic with utter confidence, alarming ignorance, minimal coherence and relentless duplicity.

President Vladimir Putin, he said, “made a living on outsmarting President Obama” — even though it is Trump who now urges a Russian return to the G-7 summit without any concessions on Putin’s part.

On pursuing the trade war with China, Trump called himself the “chosen one.” This came within hours of retweeting the claim he is loved like “the second coming of God.” At some point, arrogance is so extreme and delusional that it can only be expressed in blasphemy.

Trump accused the Danish prime minister of “blowing off the United States” because she scorned his own balmy, offensive musings on the future of Greenland. “We treat countries with respect,” he said — except, presumably, the “shithole” ones.

Trump’s new immigration rule, he claimed, would “do even more” to bring migrant families together — though this togetherness, he failed to mention, would come by allowing the indefinite detention of migrant families.

“I am the least racist person ever to serve in office,” said the man who is increasingly bold in his use of racist tropes.

He joked again about being in office 10 or 14 years from now — appealing to people who find overturning the constitutional order a laugh riot.

“Mental health,” Trump went on. “Very important.” Hard to argue with that one.

“Our 2nd Amendment will remain strong,” Trump promised, while previewing an effort to overturn that portion of the 14th Amendment guaranteeing birthright citizenship. Some parts of the Constitution, clearly, are more constitutional than others.

Trump pledged the return of thousands of captured Islamic State fighters to Europe, one way or another. “If Europe doesn’t take them, I’ll have no choice but to release them in the countries from which they came, which is Germany, France and other places.” Did the president of the United States just threaten to release dangerous terrorists on the streets of our closest allies? Evidently.

Of the wounded and grieving families Trump visited following recent mass shootings: “The love for me,” he boasted, “and my love for them was unparalleled.” And this was demonstrated by “hundreds and hundreds of people all over the floor.” No one draws a bigger crowd in an intensive care unit.

After repeating an anti-Semitic trope about the disloyalty of Jews who vote Democratic, Trump insisted to a reporter, “It’s only anti-Semitic in your head.” But control over the plain meaning of English words is not a presidential power. And the charge of disloyalty is the essence of anti-Semitism.

Seldom in presidential history has more nonsense been expressed with greater concision. Never would the interests of America have been better served by a louder helicopter.

What to make of this? First, the Trump presidency is not just unfolding; it is unraveling. All narcissists believe they are at the center of the universe. But what happens when a narcissist is actually placed at the center of the universe? The chosen one happens. Trump is not just arguing for an alternative set of policies; he is asserting an alternative version of reality, in which resistance to his will is disloyalty to the country.

Second, the president has systemically removed from his circle anyone who finds this appalling. Every president has the right to advisers who share his basic worldview. But Trump appears, on many topics, to have stopped taking advice altogether. His counselors are now flunkies. The proof of their loyalty is not found in the honesty of their opinions but in the regurgitation of his insanity.

Third, the president is increasingly prone to the equation of the national interest with his personal manias. He is perfectly willing to threaten relations with Denmark — or to force the Israeli government into a difficult choice — if it serves his tweeted whims. This approach is more characteristic of personal rule than democratic leadership. Self-worship is inconsistent with true patriotism.

Trump’s promotion of moral and political chaos puts other members of his party in a difficult position. Difficult, but not complicated. It is their public duty to say that foolish things are foolish, that insane things are insane, that bigoted things are bigoted. On growing evidence, their failure to do so is abetting the country’s decline into farce.

— Michael Gerson is a columnist for Washington Post Writers Group.