Since September 11, the federal government has drastically increased funding for immigration enforcement at the U.S.-Mexican border in the name of national security. The government has funded, among other things, complex and expensive surveillance technology and many new border patrol agents. But we lack a measure of performance. Have costly border enforcement measures actually made us safer from a terrorist threat?

At the Mexican border the government is using a deterrence-based approach to stemming undocumented migration. More border militarization and more apprehensions of migrants, the theory goes, deter future migrants seeking to cross the U.S.-Mexican border and thus decrease overall undocumented migration. Reducing unauthorized migration, in turn, is presumed to lessen the likelihood that a would-be terrorist will cross the border.

The government has spent billions of dollars on its deterrencebased model. It has implemented, on a pilot basis, technology to track the hundreds of thousands of individuals who enter the United States each year. The government has also increased spending for law enforcement agents at the border. From fiscal years 1993 to 2005, the Border Patrol budget quadrupled from $362 million to $1.4 billion, and the number of Border Patrol agents nearly tripled.

But the available evidence indicates that the government’s deterrence-based approach has not reduced undocumented migration at the Mexican border. As Walter Ewing of the Immigration Policy Center has observed, though spending on border militarization has skyrocketed over the past decade, the pace of undocumented migration has risen during the same time period. According to the Pew Hispanic Center, the number of undocumented migrants—including those who cross the border without papers and those who overstay valid visas—increased from about 400,000 annually between 1990 and 1994 to 850,000 between 2000 and 2005.

Before pouring additional money into deterrence-based border enforcement in the name of national security, we should ask whether enforcement works. Common sense suggests that individualized, human intelligence about a few potential terrorists is more effective than broad-scale border enforcement that targets hundreds of thousands of migrants. However, if government border policy is based on a desire to reduce undocumented migration from Mexico for its sake alone, then national security should not be part of the discussion.

At a minimum, without clear goals and performance measures, we cannot know whether our border efforts have improved national

security. All we know is that our government has spent a great deal of money. And the cost of the government’s border policy extends beyond dollars and cents. Increased border enforcement has made it more difficult and dangerous for migrants to cross. More border personnel and technology have led to an expansion in immigrant smuggling, already a very profitable business. Undocumented migrants pay thousands of dollars to make the increasingly dangerous crossing into the United States. The combination of demand for cheap labor in the United States, few channels for legal migration, and poor economic conditions in Mexico and Central America results in a steady stream of migrants who are willing to pay high fees and risk their lives to cross our border for better opportunities. A recent Government Accountability Office (GAO) study found that migrant deaths doubled at the southwest border during the 1995 to 2005 time frame, mainly due to deaths occurring in the Arizona desert.

The notion that deterring immigration works because we have not suffered another tragic attack is not enough. This kind of rhetoric appeals to our emotions, not our intelligence. Of course, emotion has always been a large part of our immigration policy. To some extent, deciding whether to admit an immigrant is about deciding whether we want to welcome the individual into our national community. But, when the stakes are so high, we should not let the emotions about immigration policy guide our efforts to ensure national security. We should have a clear understanding of whether our government has implemented a fiscally responsible, sustainable, and effective policy to prepare for future terrorist attacks.

It is time for a performance evaluation on national security and border enforcement at the U.S.-Mexican border. If a deterrencebased border policy does not make us safer, we should abandon our approach.