President Donald Trump announces the Air Traffic Control Reform Initiative in the East Room at the White House in Washington, DC, on June 5, 2017. Nicholas Kamm | AFP | Getty Images

On two questions over the past week, President Donald Trump illuminated aspects of his character so different from his White House predecessors that Americans have been slow to fully appreciate them. The first question, arising from the administration's withdrawal from the Paris climate agreement, was whether the president believes climate change is a genuine problem or a hoax as he previously claimed. Behind the White House refusal to answer was a simple reality: On issues of public policy, Trump does not have beliefs in any conventional sense. The second question was why Trump, after terror attacks in London, would use Twitter to attack that city's mayor and complicate the legal defense of his executive order on travel involving six majority-Muslim countries. The answer: In lieu of beliefs on policy, Trump has impulses — and feels compelled to express them whether they advance his larger goals or not.

Changing positions, again and again

Elizabeth Spiers, former editor of a newspaper owned by Jared Kushner, recently recounted an episode that paints the same portrait. The president's son-in-law, Spiers said, told her Trump didn't believe his "birther" attacks on President Barack Obama, but added "he just knows Republicans are stupid, and they'll buy it." The White House press secretary himself suggested a similar explanation for candidate Trump's Obama-era claims that the government falsified unemployment statistics. After an encouraging report this March, my colleague Eamon Javers asked whether Trump still disbelieved the data. "I talked to the president prior to this and he said to quote him very clearly," Sean Spicer said with a smile. "They may have been phony in the past, but it's very real now." The same reasoning can explain Trump's reticence on climate change. Once he wooed conservatives by claiming the problem is a Chinese hoax; disavowing that claim now could alienate core supporters. Yet repeating it would expose the president to further embarrassment on the world stage. He hasn't.

Four recurring behavioral impulses

At the same time, Trump displays consistent behavioral impulses that, for better or worse, he won't or can't restrain. One is wielding grievances to seek every scrap of advantage from interactions with others. In business, he squeezed small subcontractors over work invoices; as president, he complains that NATO members, trade partners and signatories to the Paris climate accord bilk the United States.

A second is resentment toward financial or political "elites." In business, that propelled his move from Queens to Manhattan's glitzy real estate market. In the campaign, it fueled denunciations of "politically correct" adversaries that cemented his bond with white working-class voters. A third is his instinct for racial solidarity. As president of Trump Management, he was accused by the federal government for excluding blacks from company properties; he called the charges "ridiculous" but settled the government's lawsuit. As a candidate, he complained that the Mexican ancestry of the federal judge overseeing his Trump University fraud case precluded a fair trial. In the name of preventing terrorism, he called for banning Muslims from entering the country. A fourth impulse is his professed determination to retaliate against adversaries of any kind — trying to hit harder than they had ever hit him.

Attacking the mayor London after a massacre

Those impulses merged to produce the president's tweetstorm on Monday following the London terror attacks. Trump accused his own Justice Department of making a bad deal in revising the initial executive order on the entry of people from certain Muslim countries. He mocked the "politically-correct" aversion to calling the order a "travel ban" — capitalizing the words for emphasis. He attacked London Mayor Sadiq Khan, a Muslim who had previously criticized him, even as the mayor was coping with terrorism. The president did so by misrepresenting the mayor's attempt to calm Londoners.