In March, then-Department of Homeland Security Secretary John Kelly attributed the drop in border crossings to the new policies rolled out under President Trump. “Since the Administration’s implementation of Executive Orders to enforce immigration laws, apprehensions and inadmissible activity is trending toward the lowest monthly total in at least the last five years,” Kelly said in a statement. Then, in November, U.S. agents caught 7,018 families, an increase from 4,839 the month before, according to CBP. The number of apprehensions of unaccompanied children also increased.

While it’s not the first time the U.S. has tried to discourage migrants from making the trek to the southern border, the proposed measure raises questions about the effectiveness of deterrence policy and how far an administration is willing to go to keep migrants at bay.

The United States has long relied on deterrence policy as a way of dissuading migrants from entering the country illegally. This has been true under Democratic and Republican administrations alike. In 2014, following a surge of Central American migrants at the U.S.-Mexico border, the Obama administration tried to discourage migrants from heading to the border through an ad campaign. Customs and Border Protection warned anyone considering coming north that it was too dangerous and that entering illegally would preclude them from obtaining legal status.

To some degree, it’s also what administrations try to achieve with deportations. By facing the threat of deportation, and with that, possibly being separated from their family, migrants may be less likely to try to cross the border. Immigrant advocates criticized Obama for adopting this strategy in 2016. And it’s what the Department of Homeland Security appeared to be doing when it reversed the Obama administration priority system to cast a wider net on undocumented immigrants eligible for deportation. (Overall, the number of removals decreased in fiscal year 2017 compared to the previous year, though arrests increased.)

But what deterrence policy, or any attempt to stoke fear among migrants, may not take into account are the circumstances in their origin countries that drive migration in the first place. “It’s hard to think that a family—a mother fleeing with her children who is quite literally trying to save their lives—is going to be deterred by being separated from her children,” said Maureen Meyer, the director for Mexico and migrant rights at the Washington Office on Latin America.

The factors that drive migrants to come to the United States differ for each individual. Some migrants may be seeking economic opportunity, while others are fleeing violence. The difference is that one group might be more willing to stay back than the other. “People who could afford to wait it out, do so,” Meyer said. “But those fleeing violence continue to seek protection in the United States and other countries in the region.”