The debate is between “walls” and “bridges,” but both sides would turn away most prospective immigrants. Should they? Illustration by Brian Stauffer

A hundred and seventy-four refugees from Syria arrived in Indiana, during the past fiscal year, as part of President Obama’s stated goal of admitting ten thousand Syrians who had been displaced by civil war. There were organizations in Indiana ready to help them, including a nonprofit state-supported group called Exodus. But the state itself was less hospitable: the governor publicly declared the refugees a security risk, and announced that Indiana would refuse to reimburse Exodus for any costs incurred on the Syrians’ behalf. Exodus sued, and the case was argued before the Seventh Circuit Court of Appeals last month, by which point it had acquired additional political significance: the defendant, Governor Mike Pence, was also the Republican nominee for Vice-President.

During oral arguments, the state’s lawyer was subjected to withering questions from the judges, who wondered whether barring Syrians was an efficient anti-terrorism strategy. (The state cited James Comey, the director of the F.B.I., who had acknowledged that his agency faced a particular “challenge” in checking the backgrounds of Syrian refugees.) One judge asked, “Are Syrians the only Muslims Indiana fears?”

But the judges also seemed unconvinced by the claim that Indiana was in violation of the Civil Rights Act, which outlaws discrimination based on national origin. The U.S. immigration system has long imposed national caps, meant to control not just the size of the immigrant population but its composition, too. “If the President can decide, based on national origin, how many refugees there are,” Frank Easterbrook, one of the judges, asked, “why can’t a state?”

The court eventually ruled that when it comes to immigrants it is the federal government that has the right to discriminate, not state governments. Even now, U.S. immigration rules hold that immigrants “affiliated with” the Communist Party are “inadmissible.” And countless prospective entrants are turned away each year without being given a reason, or the opportunity to ask for one.

What, exactly, are our obligations to people in other countries who would like to come to this one? The argument over Syrian refugees is a good example of how our political conversation tends to sidestep this thorny issue. Ironically, strong opposition from Republicans made it easier for President Obama to avoid explaining how he had determined that ten thousand, not more, was the proper quota for Syrian refugees. Were there security concerns that prevented the U.S. from admitting, say, a hundred thousand? How many Syrian refugees—an estimated five million have fled the country’s civil war—would be too many? Obama didn’t have to entertain questions like these, airily insisting that “refugees can make us stronger,” and claiming, not implausibly, that some of his political opponents seemed to be deficient in “common humanity.”

For much of this year, of course, Obama’s chief political opponent was Pence’s running mate, Donald Trump, who captured the Republican Presidential nomination by giving voice to a sentiment that many Republican voters evidently believe, and that few Republican politicians are willing to express: that immigration is destroying America. A 2014 poll found that a plurality of Republican voters considered immigration to be the country’s top problem, and most Americans want immigration to be restricted or kept at current levels, not increased. In recent years, however, the leaders most supportive of such restriction have tended to be rather marginal figures, like Joe Arpaio, the renegade Arizona sheriff, and Tom Tancredo, the former Republican congressman from Colorado, whose short-lived 2008 Presidential campaign was based on a promise to stop “uncontrolled immigration.” Trump was pretty marginal, too—until he wasn’t. David Frum, the former Republican speechwriter, is a longtime supporter of immigration restriction, but no fan of Trump. He once summed up the immigration debate by paraphrasing an old description of the English Civil War: “a battle between the Wrong but Wromantic and the Right but Repulsive.”

This year, amid an unusually immigration-oriented Presidential campaign, a couple of skeptical scholars are trying to arrive at an analysis that is neither wromantic nor repulsive. David Miller, a political philosopher at Oxford, sets out to answer a simple question: What gives a country the right to control its borders? Trump’s plan to build a grand, ocean-to-gulf wall may be unwise, but would it be wrong? Hillary Clinton has called for “bridges, not walls,” but she, too, wants the government to control who gets in. Miller asks when, if ever, a country is obliged to let a foreigner enter, and remain. George J. Borjas, an economist—and, as it happens, a Cuban immigrant—has a different approach. Instead of asking what we owe immigrants, he wants us to think more clearly about what we’re likely to get in return. Unlike Trump, he isn’t convinced that immigration is an existential threat to America, but he is not convinced, either, by politicians’ constant assurances that immigration is what makes America great. He believes that we should take up a question that is sometimes considered taboo: What if immigration isn’t good for us, after all?

When Trump, at the launch of his campaign, mentioned Mexican “rapists,” he was amplifying a claim made by Ann Coulter, the pundit and provocateur. Two weeks before, Coulter had published a sharp, calculatedly obnoxious polemic called “¡Adios, America! The Left’s Plan to Turn Our Country Into a Third World Hellhole.” Perhaps the most influential political book of the 2016 campaign, it is full of gruesome anecdotes about sexual assaults committed by unauthorized immigrants. Studies find that immigrants, as a group, commit fewer crimes than natives, but some data sets tell different stories. (One government report suggests that, in California, for instance, unauthorized immigrants are overrepresented in the prison population.) In Coulter’s view, that scarcely matters: any crime committed by an immigrant is one crime—and one immigrant—too many. She declares that “the rape of little girls isn’t even considered a crime in Latino culture.” (In most of Mexico, she notes, children as young as twelve can legally consent to sex with adults.) Just as confidently, she suggests that no one really likes mariachi bands. And she calls for “an immigration policy that benefits Americans.” Like Trump, who seeks to put “America First,” Coulter believes that the U.S. government has a duty, too often unfulfilled, to give priority to the well-being of its own citizens.

Miller calls this notion “compatriot partiality,” and he argues that it is a powerful principle, though one with limits. His new book is “Strangers in Our Midst” (Harvard), a lean and judicious defense of national interests. “Justice permits us to do less for would-be immigrants than we are required to do for citizens,” he writes. “But less is not nothing.” There is, he notes, a widely accepted universal right of exit—regimes that forbid defection are rightly seen as oppressive. But no government recognizes a universal right of entry. Miller thinks that this makes sense, because liberal democracies must uphold “quite demanding standards of equal treatment for all who reside within their borders.”

Such treatment might be difficult, or expensive. In the United States, all immigrant children can attend public school, and anyone accused of a crime is entitled to a legal defense, regardless of immigration status. In Miller’s view, controlling immigration is one way for a country to control its public expenditures, and such control is essential to democracy. He further suggests that “more culturally homogeneous” countries, like Japan, have a right to “protect their inherited national cultures” by restricting immigration. For him, borders are vital to democratic self-determination, particularly since immigration can change the character of a country—“the ‘self’ in ‘self-determination,’ ” he calls it. Miller thinks it is worse for a government to keep a temporary worker “in limbo” indefinitely (and so create a “two-caste” society) than to enforce immigration restrictions in a timely manner. But, in the case of refugees, he perceives a double vulnerability: by applying for asylum, a refugee “makes herself vulnerable” to a state, while imposing on the state a “duty of care.” The state is thereby obliged to accept as many refugees as it can.