In March, the American Civil Liberties Union filed a lawsuit challenging the Trump administration’s policy of detaining undocumented migrants who cross the border illegally — including those seeking asylum — and separating them from their children. When asked about the policy at a May 16 Senate committee hearing, Department of Homeland Security Secretary Kirstjen Nielsen defended it as simply following the law.

“If you are a parent or you are a single person or you happen to have a family, if you cross between the ports of entry, we will refer you for prosecution,” Nielsen said. “You have broken U.S. law.”

Some commentators argue that separating parents from their children is too high a price to pay for reducing unauthorized immigration. The UN Refugee Convention clearly states that asylum-seekers should not be penalized for entering a country illegally. But there’s another important question: Are these policies meant mainly as deterrence — and if so, does it work?

What is ‘migration deterrence’?

The idea behind deterring unwanted immigration follows from the belief that employment opportunities “pull” migrants to a given country. The logic extends far beyond the job market, however, to include any number of potential benefits a person could receive by migrating: safety, welfare, political rights, family reunification and more.

The flip side of this “pull” theory is the idea that you can reduce immigration by removing those incentives. This can work in two ways: by increasing the costs of migrating and by reducing the likelihood that immigration attempts will succeed. We can see the latter in practice across the developed world today in the form of aggressive border control, interdiction at sea and denial of legal support for people seeking asylum.

Detaining migrants crossing the border illegally and separating them from their children could be viewed as a deterrence policy of the first type: increasing the costs of migration. Having one’s children taken away is a high cost. At the same time, the second mechanism is also at work here: reducing the likelihood that immigration will be successful.

Does trying to deter immigrants work?


A Central American migrant, holding a child, looks through the border wall toward a group of people gathered on the U.S. side, as he stands in Tijuana, Mexico, on April 29. (Hans-Maximo Musielik/AP)

The effectiveness of deterrence is notoriously difficult to measure; it is hard to isolate its effects from the other factors that drive migration. But researchers increasingly find that deterrence has only a weak effect on reducing unauthorized immigration.

Overall, interdiction and detention practices do seem to reduce asylum-seeking. Some research shows that tougher policies against asylum seekers reduce the overall number of asylum applications in a country, especially over longer periods of time.

But these policies come at considerable cost for the government using them. Australia, for example, spends nearly 10 times as much money holding asylum seekers in offshore detention than it would if it allowed them to live in the community while their status was being determined.

Using family separation as a means  of preventing unauthorized border crossings, however, does not have a clear record of success. Vox reported this month that a 2017 family separation pilot program was actually followed by an increase in the number of family crossings in El Paso, where it was rolled out. Of course, this does not mean that the policy caused more families to enter the country illegally. But it does call into question whether family separation deters unauthorized immigration.

Perhaps more important, deterrence does not seem to stop migration so much as redirect it. After an unprecedented number of migrants died while crossing the Mediterranean to Europe in 2014, the European Union tried to discourage such migration by sending out fewer humanitarian sea patrols­ — which meant that attempting to cross was even riskier — and more stringently policing movement and immigration for those on the continent. The result was that Mediterranean crossings dropped slightly. However, crossings via the alternative “Balkan Route” through Greece ticked up sharply.

Indeed, research on border control has shown that efforts to obstruct or deter border crossings by constructing physical barriers or intercepting migrants at sea have primarily redirected migration flows toward increasingly dangerous alternative routes. And such policies actually appear to encourage migrants to hire human traffickers to guide them through.

If it’s not very effective, why do policymakers do it?

All developed democracies have signed international agreements promising not to send away potential refugees without first finding out whether they need protection — whether, in other words, they are seeking asylum from harm, not merely hoping for a better or more prosperous life. Such protections for asylum seekers make it difficult for policymakers to turn away people who may have a legitimate case for protection. And though they routinely violate it in practice, most governments have committed themselves to the principle of not returning migrants to a place where they will face political persecution.

But rather than risking the possibility that its own courts will offer asylum, some governments — like Trump’s — gamble that they can reduce applications in the first place by scaring migrants away. My own research shows that in countries where the courts have more control over deciding who receives asylum, policymakers are more likely to try to control immigration through deterrence.

As Michelle Brané and Margo Schlanger pointed out here at TMC, family separation is meant to be punitive. For an administration that has made no secret of its hostility to immigration, punishing unauthorized migrants may be a good in and of itself. But it isn’t clear that it is an effective policy tool.

Anna Oltman is a PhD candidate in political science at the University of Wisconsin-Madison.

Correction: A previous version of this post said that Department of Homeland Security Secretary Kirstjen Nielsen had defended the Trump administration policy of detaining undocumented immigrants and separating them from their children as being “for the purpose of deterrence.” Nielsen in fact had testified at a Senate Homeland Security and Governmental Affairs Committee hearing that DHS had not been directed to enact the policy as a means of deterrence. The post has been updated.