But for most everyone else in America, the boundaries of freedom have contracted. A whole generation may never recover from the Great Recession that followed the financial crisis of 2008. Social mobility is stagnant. And there is a growing sense — as vast stretches of the American West burn, as millions of trees die, as the acidifying oceans fill up with plastic and as species disappear — that the world stands on the precipice of catastrophe.

It might be tempting to think that President Trump’s border wall represents a more accurate, hard-bitten assessment of how the world works. The frontier was, after all, a mirage, an ideological relic of a naïve or dishonest universalism. There were, in fact, limits and costs to America’s seemingly unstoppable growth. The border wall, in contrast, is a monument to disenchantment, to a brutal geopolitical realism: Racism was never transcended; there’s not enough wealth to go around; not everyone in the global economy can have a seat at the table.

In a nation like ours, founded on a cult of exceptionalism — a belief that the country was somehow exempt from the burdens of history — the realization that life isn’t limitless was bound to be traumatic. It was also bound to produce, in the symbol of a wall, its own governing illusion.