Mr. Hazony gave no hint as to how this might be peacefully done within the scope of normal liberal-democratic politics. “It’s not simple,” he eventually conceded. Mr. Hazony notably omitted to mention, much less to condemn, the atrocious cruelty of America’s existing nationalist regime. Indeed, roaring silence around our Trumpian reality was the conference’s most consistent and telling theme.

The incoherence of an American nationalism meant to “conserve” an imaginary past was not lost on everyone at the conference. Patrick Deneen, a political theorist at Notre Dame, pointed out that American nationalism has historically been a progressive project. The nationalism of Theodore Roosevelt and Woodrow Wilson, he noted, arose as the United States began to establish itself as an imperial power of global reach. Building nations has always been about building armies, regimenting the population and centralizing political control.

Yuval Levin, the editor of National Affairs, similarly observed that nationalist projects meant to unite the diverse tribes and cultures of large territories generally involve a program of political mythmaking and the state-backed suppression of ancestral ethnic and community identities.

Mr. Levin suggested that a genuinely conservative nationalism, in the context of a vast national territory with an immense multiethnic population, would refrain from uprooting these traditions and communities and seek instead to preserve them in a vision of the nation as “the sum of various uneven, ancient, lovable elements,” because we are “prepared for love of country by a love of home.”

But what, today, do Americans call “home”? The next logical step would be to observe that the contemporary sum of rooted, lovable American elements includes the black culture of Compton, the Mexican culture of Albuquerque, the Indian culture of suburban Houston, the Chinese culture of San Francisco, the Orthodox Jewish culture of Brooklyn, the Cuban culture of Miami and the “woke” progressive culture of the college town archipelago, as well as the conservative culture of the white small town. But Mr. Levin, a gifted rhetorician who knew his audience, did not hazard this step.

Barack Obama claimed resounding victory in two presidential elections on the strength of a genuinely conservative conception of pluralistic American identity that embraced and celebrated America as it exists. Yet this unifying vision, from the mouth of a black president, primed the ethnonationalist backlash that put Mr. Trump in the White House.

The molten core of right-wing nationalism is the furious denial of America’s unalterably multiracial, multicultural national character. This denialism is the crux of the new nationalism’s disloyal contempt for the United States of America. The struggle to make good on the founding promise of equal freedom is the dark but hopeful thread that runs through our national story and defines our national character. It’s a noble, inspiring story, but the conservative nationalist rejects it, because it casts Robert E. Lee, and the modern defenders of his monuments, as the bad guys — the obstacles we must overcome to make our nation more fully, more truly American.