Surely one of the most memorable campaign promises of the current presidential election cycle—perhaps one of the most memorable ever—is Donald Trump’s promise to combat illegal immigration by building a wall between the United States and Mexico, and making Mexico pay for it. Two factors working in combination make it memorable: it is both (1) absurd and (2) popular. We are of course accustomed to hearing politicians promise things we know they are unlikely to deliver. But it is rare to hear them promise things we know are impossible to deliver, things a president has no power to deliver. Trump’s is a through-the-looking-glass kind of promise, and it has been widely ridiculed for just this reason. Yet neither the ridicule nor the impossibility of the thing promised has prompted Trump to renounce his wall. To the contrary, he has repeated the promise multiple times, and he seems to lose nothing in popularity by doing so.

Clearly he has struck a chord. Something about the immigration issue resonates deeply with many citizens. In response to recent Gallup polling on the question, “What do you think is the most important problem facing this country today?” immigration has ranked as voters’ ­second-most important non-economic concern for the past several months (except for a brief spike in concern over “terrorism” in December 2015). It is outranked only by “dissatisfaction with government,” a complaint that may well reflect many of the same anxieties felt by those who name immigration as their chief concern. Immigration has often been a heated issue in American politics. At the turn of the twentieth century, those on the Left, especially labor unions, often condemned immigration for bringing in cheap labor to compete with American workers. In recent decades, at least since Peter Brimelow’s 1992 National Review cover story, “Time to Rethink Immigration,” opposition to immigration has been an important issue among many conservatives. But immigration has captured the public imagination and shaped public discourse during the 2016 presidential campaign to a surprising extent.

Why does the issue of immigration have such resonance with voters? (And perhaps we should add, resonance with voters who support immigration as well as ones who oppose it.) It is tempting to look toward economic factors for an explanation. Middle-class wages have stagnated. Globalization leaves many workers threatened, especially in traditional industrial occupations. Even as the US economy has slowly climbed out of a recession, unemployment has remained stubbornly persistent and many people have left the job market altogether. (It is no accident that Trump has also promised tariffs on foreign imports, playing to the same fears about jobs.) The litany is familiar.

I doubt, however, that economic factors alone can adequately explain immigration’s pull on the American political psyche. Trump’s unrealizable wall is not so much a real policy proposal as it is a symbol. Indeed, Americans are less concerned about the economy than they have been for most of the past decade. The net percentage of Americans in Gallup’s polls “mentioning economic issues as the nation’s most important problem” has declined from a high of 86 percent in early 2009 to only 39 percent at present, a drop of more than half. Economic anxiety surely explains some of the concern over immigration. But more is at stake.

Immigration is not like most other political issues that we debate. We can argue about whether it is a good idea to compel Apple to unlock a cell phone tied to the San Bernardino terrorist attacks. We can consider whether it would help lower healthcare costs if we permitted insurance companies to compete across state lines. We can ask whether the cost of college should be subsidized, whether Common Core standards will improve educational outcomes, or whether we should supply Syrian rebels with training and arms. What kind of judge do we want appointed to fill Scalia’s seat on the Supreme Court? Will we balance the budget more successfully with this or that candidate’s tax plan? Should we raise the retirement age?

Such arguments are the bread and butter of partisan politics. Yet they all differ in one fundamental respect from debates over immigration. Lurking behind all of these disputes is the taken-for-granted little pronoun “we.” What should “we” do about terrorism, health care, taxes? In almost every political debate, the content of that “we” is simply assumed—we Americans, we voters, we citizens. But when we debate immigration, this is no longer the case. For unlike those other issues, immigration policy is about determining the nature of that “we” itself, about determining who we are in the first place. There may be a small number of other issues that raise this question also. Two that come to mind are the great historic fights for full civic inclusion: the women’s suffrage movement, and the struggles against slavery and Jim Crow. But no other contemporary issue goes in the same way to the question of who “we” are.

The political philosopher Michael Walzer captured this point nicely in a book about distributive justice entitled Spheres of Justice (1983). The book’s central argument is that principles of distributive justice vary depending upon the particular good being distributed and the social purposes it is thought to serve. We distribute wealth for certain reasons, education for others, honor or political power for still others. Because these are different kinds of things, we treat them differently—the reasons I might deserve to hold political office are not the same as the reasons why I deserve an education, or medical care, or love and affection. Before discussing any of these various goods, however, Walzer begins with a chapter discussing a still more fundamental good: “membership,” under the heading of which he analyzes both immigration and naturalization. “The primary good that we distribute to one another,” he writes, “is membership in some human community. And what we do with regard to membership structures all our other distributive choices: it determines with whom we make those choices, from whom we require obedience and collect taxes, to whom we allocate goods and services.” The question of membership precedes all other decisions we make by identifying who “we” are to begin with; it is therefore “the first and most important distributive question.”

Because membership is the primary good that we distribute to one another, immigration is linked to one of the most basic functions served by any government. The chief purpose of government, no doubt, is to ensure peace and security—in traditional Christian language, to punish the wicked and protect the innocent. But a second essential function of government is to represent the people (citizens, subjects) it governs. This is as true of a monarchy as it is of a democracy. Every government, at least in the modern world, claims to stand for, to re-present, the will of its people. Hobbes described this in vivid contractual language when he claimed that all subjects agree to regard themselves as the “authors” of their sovereign’s actions. Our government speaks for us; we are, all of us (re)present(ed) in its actions.

Immigration is thus a peculiar political issue, because in crafting immigration law and policy, our representative agent reconstitutes the very “we” from which its authority derives. Understanding this helps explain why immigration becomes such a symbolically charged issue for those who feel threatened by it. For if one of government’s essential functions is to represent “our” will, how does it justify granting the tremendously valuable benefit of membership to outsiders while we, or many of us, face hardship? And what are we to think of those people—our own fellow citizens!—who support further immigration and thus also subordinate our interests to those of outsiders (or, perhaps, to their own self-interest)? This dynamic helps explain why the improbable Trumpean wall resonates so powerfully with so many voters, citizens who no longer believe that their government truly represents them, or their values, or their interests.

I should emphasize that I am not here attempting to argue that large numbers of American voters are in fact harmed, economically or otherwise, by immigration. Nor am I claiming that immigration is bad for the country. Nor am I forgetting that many Americans support immigration and want no part of a wall. My own views on the issue fall toward the middle of the political spectrum. I am simply trying to understand why the immigration issue seems to have so powerfully captured our political imagination. And for that purpose I believe we need to look deeper than mere economic unease, deeper than the question, for example, of whether immigration creates a net gain or loss in GNP or causes a net gain or loss in number of jobs created. Instead, we need to understand that immigration, because of its intrinsic links to membership and representation, is not like other political issues.

Grasping these connections is important not only in order to understand or empathize with opponents of immigration or voters who cheer proposals for a wall. It is also important for those who desire more immigration. For except in cases of refugee admissions—cases where we may genuinely be arguing almost entirely about the needs of others, with our interests well in the background—pro-immigration arguments no less than restrictionist ones presume and make claims about the “we” of our polity. If immigration brings economic benefits, it is “our” economy that receives those benefits. If it reunites families, they are “our” families, or at least families with a foothold among us and in our communities. If it enriches the culture, then “our” culture enjoys that enrichment. For better or for worse, immigration is always about who we are and who we will be in the future.

It is perhaps especially important to remember this in times of uncertainty and turmoil, or of what Gallup called general “dissatisfaction with government.” Generosity toward outsiders and a readiness to view them as potential fellow members whose participation in the political community would enrich our own lives almost surely requires as a prerequisite an underlying confidence among “us” that our representative is indeed attending to our best interests. In a book called Irish Impressions—having nothing to do with immigration—G. K. Chesterton makes this point very nicely. He speaks there of the “law of leisure needed for the awakening of wonder,” and he suggests that borders are important not simply as a defensive measure, but also because they make the true flourishing of human diversity, both within communities and among them, possible. “The chief case for old enclosures and boundaries,” he writes, “is that they enclose a space in which new things can always be found later, like live fish within the four corners of a net. The chief charm of having a home that is secure is having leisure to feel it as strange.”

Neither Donald Trump nor any other successful presidential candidate is going to force Mexico to pay for a new border wall. But without attending to the true reasons why that impossible promise appeals to many voters, it will only become more difficult to resolve our disputes about immigration. To steal a line from Robert Frost: Something there may be that doesn’t love a wall. But citizens who cease to feel that our government speaks for “us,” who increasingly feel their home only as strange and never as secure, will surely conclude that good fences make good neighbors.

Peter Meilaender is Professor of Political Science at Houghton College.