At this juncture, she argued, we need to tinker with that balance and get it right for everyone. So there’s the paradox of our times: it is likely that rather less liberal democracy will ultimately make liberal democracy more secure.

Among liberals, Stenner argued, the greatest ambivalence “attaches to immigration issues,” and that ambivalence is only worsened by the unwillingness of liberals to accept an open debate in which immigration opponents can “express their fears and concerns, without being called racists.”

Suzette Brooks Masters — who has written extensively about immigrant integration, detention, employment-based immigration and the immigrants’ rights field generally — made a parallel point in her recent study of immigration, “Change is Hard”:

Academics agree that it is the pace of change relative to the composition of the receiving community that matters most. Simply put, if a place is already quite diverse, making it more diverse matters less. Even significant inflows of diverse newcomers will be perceived as less threatening because the community has already adapted to greater diversity. By contrast, in a relatively homogeneous location, even small absolute numbers of newcomers, such as refugees, can be disruptive and activate cultural anxiety.

Jonathan Haidt, a professor at NYU’s Stern School of Business, offered a similarly nuanced examination of how the balance between tribalism and openness might play out. Tribalism, he wrote by email,

is not a mindless and eternal “us versus them” mentality. It is a set of psychological adaptations that make people respond to threats and intergroup competition with an urge to band together, enforce loyalty to the team, and guard boundaries or territory.

In the political arena, Haidt continued,

if one gains prestige for outdoing others on one’s devotion to sacred values — such as guarding America’s borders, on the right, or being antiracist on the left — then the party’s rhetoric will shift to the extremes, with candidates making more extreme proposals that gain them prestige.

The pressures to go to extremes, Haidt suggested, are “roughly symmetrical between left and right.”

John R. Hibbing, a political scientist at the University of Nebraska, takes a more uncompromising stance. In an email, he wrote:

Though consideration of such matters is always speculative, suggesting the possibility that conservative orientations, particularly on topics such as immigration and race, are evolutionarily more primal is perfectly reasonable.

In their book “Predisposed: Liberals, Conservatives, and the Biology of Political Differences,” Hibbing, Kevin B. Smith, of the University of Nebraska, and John R. Alford, of Rice, argue that liberalism is “an evolutionary luxury” that can emerge in people when “negative stimuli becoming less prevalent and less deadly,” or, as Hibbing put it in an email, “when daily threats to life and limb posed by other human beings have diminished.”

Conversely, they write, if the environment shifts back to a “threat-filled atmosphere,” then “positive selection for conservative orientations would reappear.”