In their popular song “Jaula de Oro,” which translates to “Cage of Gold,” the famous Mexican band Los Tigres del Norte tells the story of a migrant who finds himself unable to move across the U.S.-Mexico border. His lack of mobility does not keep him in Mexico, as one would expect, but in the United States. As the migrant explains:

Ten years have passed since I crossed … I’m still an illegal … My wife and my children … have already forgotten about my beloved Mexico, the one that I never forget and I cannot return to … When I remember I even cry that even if the cage is made of gold, it does not stop being a prison.

Donald Trump’s executive order to build a wall between Mexico and the United States overlooks how the fences, walls, and border-control measures that already exist between the two countries have come to act as a barrier—or a “cage of gold”—that discourages migrants from leaving the United States, rather than preventing their entrance in the first place.

Before 1986, the border was much more permeable than it is now. The Border Patrol had a very limited budget and limited personnel to handle the growing number of migrants who were entering the United States. According to Princeton University sociologist Thomas Espenshade, this meant that the likelihood that an undocumented migrant would be apprehended while trying to enter the United States was only one in three.

The porous nature of the border allowed most Mexican migrants to engage in circular migration. Most were men who would come to the United States, work here for a short period of time, return to Mexico to be with their families, and then repeat the process.

In 1986, however, the pattern of circular migration ended after Ronald Reagan signed into law the Immigration Reform and Control Act, or IRCA. Upon doing so, Reagan hailed: “Future generations of Americans will be thankful for our efforts to humanely regain control of our borders and thereby preserve the value of one of the most sacred possessions of our people: American citizenship.”

One of IRCA’s primary measures was to increase the enforcement budget of the Immigration and Naturalization Service. As a result, crossing the national boundary became a much more dangerous and expensive enterprise. To avoid detection, migrants had to pay smugglers to help them get across hazardous terrains that were less patrolled.

Despite the new hardships of migration, relatively few Mexicans reconsidered their decision to head north. On the contrary, the numbers of undocumented migrants continued to grow. While in 1986, an estimated 3.2 million unauthorized migrants lived in the United States, the number reached 5 million in 1996, and grew to approximately 11 million in 2006. Despite the increased fortification of the border, Mexicans continued going to the United States because of economic need. After all, the passage of IRCA did nothing to alter the low wages and high underemployment rates in Mexico. However, as sociologist Douglas Massey and others have shown, as crossing the border became increasingly hard after 1986, most migrants started refraining from going back and forth between the two countries and instead decided to settle permanently in the United States.

The increased fortification of the border after 1986 also altered the demographics of migration. Once men realized that they would settle in the United States, they encouraged their wives and children to head north with them. Women had traditionally refrained from migrating because they risked being sexually assaulted at the border. But their husbands now also faced much danger when they traveled to the United States. Instead of having men expose themselves to these hazards repeatedly, women started to risk the border once and head to the United States. The travel of women and children further contributed to the rise of undocumented migration in the years following 1986.

Only the Great Recession stopped and even reversed the growth of undocumented migration. After 2008, more Mexicans started returning to Mexico from the United States than those who crossed the border north. Some of them were unable to enter the United States because of the increased border enforcement in the mid-2000s that followed the terrorist attacks of September 11, 2001, while others had to leave because they were deported. But many others ceased to be interested in coming to or remaining in the United States. The slow recovery of the U.S. economy after 2008 and the decreasing number of jobs available to immigrants, particularly those in construction where many Mexicans worked, made the United States less attractive. Fewer migrants sought to risk their lives at the border to come and those who were already here but still had family members in Mexico returned home to be with them.

Trump has never acknowledged that since the Great Recession the net outflow of Mexicans is larger than the inflow, and instead, continues to insist that the wall is necessary to curtail Mexican undocumented migration. Rather than explaining how the wall will reduce unauthorized entrances, Trump has focused on his ability to build one that’s “big” and “beautiful,” and on the idea that Mexico will pay for it.

But it’s a wall that will likely reinforce the bars of the cage of gold and discourage those who are already here to continue leaving as they have done since the Great Recession. A wall that has come to symbolize a rupture in the relations between Mexico and the United States, thus increasing economic uncertainty in Mexico and, perhaps, adding to Mexicans’ need to head north. A wall that even Trump’s Homeland Security secretary asserted won’t work in deterring unauthorized border crossings as much as partnering with countries south of the border would. A wall that will do much to build racial animosity against Mexicans and Mexican Americans by equating them with illegality.