I’m not surprised. Both parties — but not the average American voter — have been moving in a globalist direction for years. In his 2013 Inaugural Address, President Obama championed the qualities of innovation and mobility that will allow our nation to thrive in “this world without boundaries.” He was not proposing to eliminate passports, but he was expressing a sentiment that regards borders, limits and boundaries as necessary but regrettable, while openness and diversity are inherent goods.

This way of thinking is everywhere, which makes it seem like common sense, rather than a political choice. Woodrow Wilson formulated Princeton’s informal motto: “Princeton in the nation’s service.” In 1996 it was extended to include “and in the service of all nations,” and then recently revised to read “Princeton in the nation’s service and the service of humanity.” Undoubtedly, administrators thought they were adapting to new global realities, rather than taking a controversial stance.

The same goes for Stanford’s president, John Hennessy, who raised $750 million to fund a new program to gather “the world’s brightest minds” who can work “toward solving global challenges.” Isn’t this an admirable, sensible and responsible adaptation to the direction things are going?

In contrast, Mr. Trump does not presume that the world must become flat. His Inaugural Address contrasted sharply with Mr. Obama’s 2013 speech. He spoke of renewing borders and solidarity, and called for national reconsolidation. This does not mean putting a stop to global trade or shutting down immigration, any more than Mr. Obama meant to bargain away American sovereignty or “destroy America,” as some conservative pundits insisted during his administration. But these two speeches, only four years apart, reflect a stark difference in emphasis. What Mr. Obama presented as a happy evolution Mr. Trump frames as something to be resisted. As he said in his recent address to the joint session of Congress: “My job is not to represent the world. My job is to represent the United States of America.”

Mr. Trump’s shocking success at the polls has done our country a service. Scholars may tut-tut about the historical connotations of “America First,” but the basic sentiment needs to be endorsed. Our country has dissolved to a far greater degree than those cloistered on the coasts allow themselves to realize. The once vast and unifying middle class has eroded over the last generation. Today we are increasingly divided into winners and losers. This division involves more than divergent economic prospects and income inequality. Globalism is an ideology of winners who stand astride our society as it is being remade by dramatic economic, demographic and cultural changes.

Mitt Romney wrote off nearly half the American population as “takers.” Hillary Clinton made her notorious remarks about “deplorables.” These sentiments, widely shared by elites on the right and left, have become toxic. Caterpillar recently announced it is moving its corporate headquarters from Peoria, Ill., to Chicago. The unspoken reason? “C-suite level” talent bridles at relocating to flyover country. In today’s America, the rich, well-educated and globalized people on top, whether Republicans or Democrats, do not want to live among those who populate our country. The leaders increasingly hold them in disdain.

After World War II, Mr. Buckley adopted an exaggerated approach to postwar American liberalism (which was hardly inclined toward socialism) because he thought the stakes were high. We face different dangers. In 2017, a growing economic divide and continuing cultural fragmentation, and even animosity, are grave threats that now define our politics. The Cold War is now domestic. Easy talk about the world becoming flat or global trade lifting all boats disguises, explains away and exacerbates the damage being done to the body politic. Mr. Trump’s stark juxtaposition of globalism and Americanism is crude and hyperbolic, but necessarily so.