Professor Mary Hoopes, Do Border Policies Deter Migrants? -- California Law Review (forthcoming)

Professor Mary S. Hoopes's article, Do Border Policies Deter Migrants?, (SSRN) will be published in the California Law Review (forthcoming 2027). The article, co-authored with David Hausman and Adam B. Cox, examines the effectiveness of border enforcement policies on preventing migration. 

Abtract of Do Border Policies Deter Migrants?

For generations, American border policies have been driven by the claim that border enforcement can deter migration to the southern border. Most recently, President Trump has taken credit for the lowest levels of border apprehensions in decades. But this deterrence theory of border policy is behind nearly every major border initiative adopted in recent decades, including Presidents Clinton’s militarization of the border, President Obama’s dramatic expansion of family detention, President Trump’s family separation policy, and President Biden’s suspension of the asylum system along the U.S.-Mexico border. Deterrence theory also permeates political debate over immigration policy. While the Republican and Democratic parties have clashed sharply over immigration policy in the last generation, the one thing on which they have consistently agreed is that border enforcement policies prevent migration.

But do they? Despite the governing framework, we know far too little about the extent to which policies designed to deter people from crossing the southern border actually do so. This Article corrects that deficiency. Assembling a dataset of more than ten million Border Patrol apprehensions, we measure the short-term effects of nearly every major border policy innovation since 2014—including policies separating families or detaining them, policies tightening access to asylum or closing the border altogether, and policies that require people to apply for protection from their home countries rather than at the southern border.

Our study yields two critically important findings. First, there is little evidence that discrete border enforcement policies have had significant short-term effects on whether people come to the United States. Second, there is strong evidence that border policies affect how migrants choose to enter—for example, whether they travel through ports of entry or try to evade inspection, and whether they apply for admission from their home countries or at the border. Together, these findings suggest that policymakers should be more skeptical of deterrence theory and more focused on the capacity of border policies to affect the time, place, and manner of entry.

This conclusion has important implications for the efficacy and humanity of border policy. This Article suggests that the faulty logic at the heart of American border policy has produced perverse results, driving migrants into the desert and away from ports of entry even as policymakers’ asserted goal is to reduce unlawful border crossings. Our study also suggests that carrots are more effective than sticks when trying to increase compliance with immigration law—a crucial finding in our present political moment, as the Trump administration doubles down on a sticks-only immigration enforcement strategy.