The most troubling feature of contemporary American politics is no longer polarization alone, but the gradual normalization of ideas that once existed at the margins of public life. In the years since Donald Trump reshaped the Republican coalition, the party has struggled to define what it stands for beyond grievance and cultural resentment. That struggle is now increasingly visible in the rise of JD Vance, who has positioned himself as both Trump’s heir and a bridge between mainstream conservatism and openly extremist currents.

Mr. Vance presents his project as inclusive and pragmatic, a “big tent” populism grounded in economic nationalism and social conservatism. Yet his rhetoric and alliances suggest a different dynamic at work. By refusing to draw firm moral boundaries against white nationalist and antisemitic ideologies, he has advanced a politics that tolerates — and in practice legitimizes — exclusionary worldviews under the banner of “America First.”

That strategy was on display at recent gatherings of conservative activists, where Mr. Vance declined to condemn antisemitism directly or to distance himself from figures associated with white nationalist movements. Instead, he framed such demands as divisive “purity tests,” arguing that the movement should welcome anyone who claims to love America. On its surface, this language sounds conciliatory. In reality, it dissolves the distinction between political disagreement and ideological harm.

White nationalism is not a policy preference. It is an ideology rooted in hierarchy and exclusion. Treating it as just another viewpoint within a political coalition is not neutrality; it is permission. History offers few examples in which extremist movements are accommodated without eventually reshaping the institutions that tolerate them. When moral clarity is abandoned in the name of unity, the cost is borne by those whom such ideologies target.

Mr. Trump’s own experience illustrated this dilemma. His refusal to clearly denounce white supremacist demonstrators after the Charlottesville rally in 2017 marked a turning point in public trust. Attempting to straddle moral boundaries did not broaden his appeal; it narrowed it. Standing with racists, even ambiguously, inevitably means standing against those they exclude.

What distinguishes Mr. Vance from his predecessor is not ambiguity, but coherence. Over time, he has increasingly adopted the language and assumptions of the far right, repackaging them in polished, pseudo-intellectual terms. His praise for restrictive immigration laws of the 1920s, his arguments that Americans with deep ancestral roots have a stronger claim to the nation, and his flirtation with the concept of “heritage Americans” all echo long-standing white nationalist talking points. These claims avoid explicit racial slurs, but their logic is unmistakable: some Americans are more authentically American than others.

That framing collapses under even minimal historical scrutiny. The United States has never been defined by a single ethnicity, and the Constitution’s post–Civil War amendments explicitly rejected that idea. Yet a growing faction on the right has sought to undermine those principles by questioning birthright citizenship and the legitimacy of multiracial democracy itself. Mr. Vance’s rhetoric aligns with that movement, even as it is cloaked in appeals to tradition, Christianity and national cohesion.

At events hosted by organizations like Turning Point USA, Mr. Vance has declared that Americans no longer need to apologize for being white and that the United States “will always be a Christian nation.” Such statements are not rhetorical accidents. They signal to a base animated by grievance politics that cultural dominance is under threat — and that he is prepared to defend it.

This messaging resonates particularly with younger conservatives, among whom admiration for authoritarian leaders and ethnic nationalism has become increasingly visible. Turning Point USA’s embrace of Mr. Vance reflects a calculation that intensity matters more than breadth. With its expansive campus network and media reach, the organization offers an infrastructure well suited to mobilizing a highly loyal, ideologically rigid base.

But politics, ultimately, is about addition, not subtraction. White nationalism is inherently subtractive. Mr. Trump’s success depended in part on persuading some voters — including voters of color — that his most extreme rhetoric was performative. Mr. Vance lacks that ambiguity. His worldview is more explicit, more systematic and therefore more difficult to disavow.

Signs of strain are already evident. Even within pro-Trump Republican spaces, voices have emerged warning that ranking Americans by ancestry or race is fundamentally un-American. Those objections have often been met with hostility or silence, underscoring how far the movement has shifted — and how fragile its unity has become.

Mr. Vance may claim to be building a “big tent,” but racial hierarchy cannot coexist with genuine pluralism. The Republican Party faces an unavoidable choice: reject exclusionary ideology or be defined by it. Pretending otherwise does not create unity. It merely delays a reckoning that grows more consequential with each election cycle.