A group of sanctuary state supporters gather outside the Orange County Board of Supervisors meeting in Santa Ana, Calif., March 27. (Jeff Gritchen/The Orange County Register via AP)

Do sanctuary policies “breed crime”? That’s what President Trump charged last week when he tweeted:

Declaring that immigration is linked to crime has been one of Trump’s main themes, going back to his campaign. And last month, the U.S. Department of Justice (DOJ) sued the state of California, arguing that the state’s sanctuary laws violated the Constitution’s supremacy clause, “making it more difficult for federal immigration officers to carry out their responsibilities.” While California’s governor, attorney general and state senate leader quickly mobilized to fight back, some California cities and counties sided with the Trump administration. For instance, the Los Alamitos city government voted to exempt itself from the state policy, and last week, the San Diego County Board of Supervisors voted to support the Trump administration’s lawsuit against California.

But while Trump and others charge that these policies “breed crime” and protect criminals, supporters argue that sanctuary policies can improve public safety by making undocumented residents feel secure enough to cooperate with police — and therefore, make it easier for police to do their jobs.

So who’s right? A Washington Post fact check gave Trump three Pinocchios for his claim last year. The research that exists, including my own, suggests either that counties with sanctuary policies have less crime than comparable non-sanctuary counties, or that there is no statistically significant relationship between city sanctuary policies and increased crime rates.

But why?

Here’s how I did my research

I wanted to know whether it’s true that, when undocumented immigrants know local authorities aren’t working with Immigration and Customs Enforcement (ICE), they’re more likely to turn to and cooperate with law enforcement when they need to.

To find out, I embedded an experiment in a representative survey of undocumented Mexican nationals in San Diego County (see below for more information on the sample). The survey is part of a larger ongoing project examining how the Trump administration’s immigration policies are affecting undocumented immigrants. The interior immigration enforcement module, which includes the experiment, was fielded between September and November and includes 594 respondents.

Respondents were randomly assigned to one of two groups, both of which were asked the same questions. However, for the first group of 298 people, the questions were prefaced with, “If the San Diego Police Department and the San Diego County Sheriff’s Department said they WILL NOT WORK WITH ICE on deportation raids, would you be more or less likely to …” For the second group of 296 people, the questions were prefaced with, “If the San Diego Police Department and the San Diego County Sheriff’s Department WERE WORKING TOGETHER WITH ICE on deportation raids, would you be more or less likely to …”

You can see the list of questions — and the differences in respondents’ answers — in the table below. As the table shows, if local law enforcement officials were working together with ICE, 60.8 percent said they are less likely to report a crime they witnessed, and 42.9 percent said they are less likely to report being a victim of a crime.


Note: the asterisks indicate that these differences are statistically significant at less than the 0.001 level.

All the results are just as stark, showing the chilling effects of having local law enforcement agencies do the work of federal immigration enforcement. Fully 69.6 percent say they are less likely to “Use public services (e.g., go to City Hall) that required you to give your personal contact information”; 63.9 percent say they are less likely to “Do business (e.g., open a bank account, get a loan) that required you to give your personal contact information”; 68.3 percent say they are less likely to “Participate in public events where police may be present”; among those with children, 42.9 percent say they are less likely to “Place your children in an after-school or day-care program”; and 52.1 percent say they are less likely to “Look for a new job.”

The research suggests that sanctuary policies do not in fact “breed crime.” What’s more, enlisting local law enforcement agencies to enforce federal immigration laws can drive undocumented immigrants deeper into the shadows. Of course, that may be the administration’s goal.

Tom K. Wong is associate professor of political science at the University of California at San Diego. His most recent book is “The Politics of Immigration: Partisanship, Demographic Change, and American National Identity” (Oxford University Press, 2017).  

Note on survey

I partnered with Mexican consular officials to create a sample frame — a list of individuals from which to draw samples for survey purposes — of undocumented Mexican nationals in San Diego County. The list is composed of individuals who received consular services unique to those living in the United States without authorization. Consulates provide a broad range of services to nationals abroad. For example, an American abroad in another country who loses her passport would go to a U.S. consulate in that country to obtain new documents. The sample frame, which includes approximately 73,000 people, accounts for nearly the entire universe of undocumented Mexican nationals in San Diego County, as demonstrated by the fact that the Center for Migration Studies estimates there are 82,406 undocumented immigrants who were born in Mexico and reside in San Diego County.

Because of the vulnerability of this population, these data remain on the computers of the consulate. Working with staff at the consulate, I draw random samples of approximately 5,000 individuals for each survey module that I administer and generate random ID numbers for each individual. Call sheets with limited information about each respondent (the random ID number assigned to each record, first name, and phone number) are printed out. Phone numbers are then manually dialed by enumerators who have all signed confidentiality agreements. Numbers are dialed once, with no additional follow up, so that after a call sheet is completed, it can be quickly reviewed and destroyed. All surveys are conducted in Spanish, unless the respondent prefers to speak in English.