Because he's an imbecile

Shortly after taking office, Donald Trump asked his aides whether Ukraine, and not Russia, might have hacked Democratic National Committee emails as part of a false-flag operation. Then–Homeland Security Adviser Tom Bossert tried to stop the idea in its tracks.

“It’s not only a conspiracy theory, it is completely debunked,” Bossert said on ABC’s This Week on Sunday. Bossert brought in the director of the National Security Agency to brief Trump, according to The New York Times. The president, Bossert thought, seemed to grasp the truth.

But in July 2019, more than a year after Bossert left the White House, Trump raised the theory in a call with the Ukrainian President Volodymyr Zelensky, which resulted in a whistle-bower complaint and the release of an incriminating reconstructed transcript of the call. Now Trump’s recalcitrance has landed him in perhaps the most serious peril of his presidency, with Democrats moving forward with an impeachment inquiry, and polls showing strong public support.

The latest Trump scandal demonstrates how incapable Trump is of learning—either facts or lessons—and how dangerous that is. Trump’s refusal to accept the truth about Ukrainian hacking (which did not happen) arose from his refusal to accept the truth about Russian hacking (which did happen). That is, Trump’s obsession with Ukraine began as a search for vindication over allegations of foreign interference in the 2016 election, and led directly to Trump importuning foreign interference in the 2020 race.
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Trump’s troubles stem from a temperamental aversion to displeasing information, and an inability to sort reliable sources from bad ones. He shows notable lack of interest in his official briefing materials, which have been shrunk down to minimal form. He eagerly consumes conspiracy theories and humbug, though. Former Chief of Staff John Kelly attempted to keep bogus information away from Trump, but his successor, Mick Mulvaney, wants to let Trump be Trump—even, apparently, if that includes taking up debunked nonsense.

Trump has at his command the full information-gathering capabilities of the U.S. government, perhaps the most powerful data operation in world history. The intelligence community is not infallible, with several notable failures in recent memory, but it’s far better than the alternative: Giuliani’s credulous, harebrained solo investigations. Because Trump never accepted the reality of Russian interference despite the unanimous judgment of his own experts, he was also unable to grasp the danger in asking Zelensky to do him a “favor.” Nor did the Mueller experience teach him the dangers of attempting a cover-up.

The paradox is that the stubbornness Trump shows when he refuses to grapple with new information is tightly related to his success as a politician. During the 2016 presidential race, the search by some pundits for a “Trump pivot,” when the candidate would drop his bigoted and wild-eyed rhetoric and adopt a more somber tone, became a running joke. Trump never pivoted, because he was constitutionally incapable of it. But his consistency contributed to an appearance of authenticity that his supporters love, even though, as Gilad Edelman recently wrote, he is “an inveterate fabricator born to fabulous wealth who poses as the self-made tribune of the working class.” Obstinacy helped Trump succeed in 2016, but it threatens to cut him down in 2019.