In his unexpected announcement Thursday that the U.S. will impose tariffs on steel and aluminum imports, President Donald Trump insisted that these metals are essential to national identity. “When it comes to a time where our country can’t make aluminum and steel ... you almost don’t have much of a country,” he said. “Without steel and aluminum, your country is not the same.” This recalls a familiar refrain from Trump’s presidential campaign. “We don’t have a country without a border,” he told Joe Scarborough on MSNBC in July of 2015. “Without a border, we just don’t have a country.”

These words reveal something essential not just about the priority Trump gives to trade protectionism and immigration restriction, but the nature of this nationalism. His notion of American identity is narrow and shallow, encompassing only the country’s borders and its raw products. You take those away, and America is nothing. In short, he’s a brick and mortar (and steel) nationalist.

Earlier presidents, have spoken of America in more elevated, symbolic terms—as an idea, and sometimes as an ideal. For Lincoln, in his inaugural address, America was held together by the “mystic chords of memory, stretching from every battlefield and patriot grave to every living heart and hearthstone all over this broad land.” For Ronald Reagan, America was, as he said in many speeches, “a shining city on a hill.” George W. Bush, in his first inaugural, said, “America has never been united by blood or birth or soil. We are bound by ideals that move us beyond our backgrounds, lift us above our interests, and teach us what it means to be citizens.”

Trump will, if delivering a prepared speech, mouth similar pieties about “the self-evident truth Americans hold so dear, that no matter the color of our skin, or the place of our birth we are all created equal by God.” But this language does not come naturally; when speaking off the cuff—and tweeting—he usually talks about America in simplistic, purely physical terms.

Trump’s lack of more idealistic nationalism may be attributable to his struggles with abstract reasoning. Even very simple concepts like “all men are created equal” seem to baffle him.

“They say all men are created equal,” Trump said in a 2009 interview with Deborah Solomon for The New York Times. “It doesn’t get any more famous but, is it really true?” Solomon asked whether he thought it was true, and Trump replied, “It’s not true. Some people are born very smart, some people are born not so smart. Some people are born very beautiful and some people are not so you can’t say they’re all created equal.” Solomon lent him a hand: “They’re entitled to equal treatment under the law. I think that’s what the statement means. It doesn’t mean everybody has the same endowments.” “That’s correct,” Trump said. “The phrase is used often so much and it’s a very confusing phrase to a lot of people.”

Whether the phrase is confusing to others, it’s clearly confusing to Trump, who can only understand it in the most literal level. If people aren’t all physically equal, then the idea that they are still equal makes no sense to Trump. (It’s also clear that he thinks people are born winners or losers.)

This deficit of abstract thinking is also apparent in Trump’s views on trade. As the Toronto Star’s Daniel Dale reported, “Trump has repeatedly insisted that the U.S. actually has a multi-billion-dollar deficit with Canada. He refers only to trade in goods, in which there is indeed a U.S. deficit, and excluding trade in services, in which there is a U.S. surplus bigger than the goods deficit.” Trump seems incapable of conceiving of trade that does not involve physical objects.

Trump is a classic mercantilist for whom trade is a zero-sum game; if one country profits, then another one loses. He can’t imagine trade as a mutually beneficial relationship. This was evident in a Friday tweet:

The simplicity of Trump’s sense of national identity can make him seem refreshingly honest and focused on concrete goals—building a wall, saving the steel industry. But his brick and mortar nationalism also reveals a lack of imagination. Unlike earlier presidents, Trump isn’t trying to inspire all Americans, let alone other nations; he speaks only to his hardcore supporters, in terms anyone (even Trump) can understand. In doing so, he is shrinking the very idea of America.