Since Donald Trump entered the White House, a surprising rift has opened between the business community and the pro-business president. Many of the country’s top executives have criticized Trump for withdrawing from the Paris climate accord; for signaling his support for white supremacists; and, most significantly, for cracking down on immigration. More than 100 tech firms came out against Trump’s proposed Muslim ban. Farmers in California have expressed deep concern about his efforts to deport undocumented workers. And after Trump moved recently to undo legal protections for immigrants who came to the United States illegally as children, hundreds of business leaders denounced the policy shift. “This is not who we are as a country,” Apple CEO Tim Cook said of the plan to end the Deferred Action for Childhood Arrivals program. “If I were a country leader right now, my goal would be to monopolize the world’s talent.”

To explain why Trump has broken so dramatically with his fellow executives, commentators have pointed to the rising influence of nativism within the Republican Party. But the GOP has always hosted anti-immigration nativists; they are the descendants of the Know-Nothing Party, the virulently anti-immigration party of the 1840s and 1850s. For more than a century, however, business support for immigration kept the nativists at bay. Indeed, from the 1870s to the 1970s, Republican senators were much more pro-immigration than their Democratic counterparts.

Today, the balance has shifted. But the reason the GOP has embraced anti-immigration policies actually has little to do with rising nativism. Instead, it’s because most businesses simply don’t care about immigration the way they used to.

A major reason for the business community’s fading support for immigration has been America’s increased openness to trade and competition from the developing world. During the last era of mass migration to the United States, in the late nineteenth and early twentieth centuries, many manufacturing industries were protected by tariffs. And as these industries expanded, companies increasingly hired immigrants to help keep wage costs low. Encouraging immigration was simply good for the bottom line.

Consider the textile industry. From the 1870s to the 1940s, textiles enjoyed robust trade protection and boomed as a result. As the industry grew, it became a major employer of immigrant labor. Mills throughout the Northeast were filled with workers from Ireland, Italy, and elsewhere. And, for most of that time, the owners of the mills—and their members of Congress—were major supporters of immigration.

After World War II, however, the United States began to dismantle many of its trade barriers. Competition from developing countries, particularly China, also increased as they opened their markets to exports. Technological advances in shipping, especially the rise of the container ship, only exacerbated these trends by dramatically lowering the cost of transporting goods overseas. About 30 percent of manufacturing firms, from textile and steel mills to car and toy companies, could not compete and closed their doors. Since the 1990s, the textile industry has shed almost 70 percent of its workforce, and today textiles are mostly produced abroad. Without the pressure these companies put on lawmakers to maintain open borders, the Republican Party has been increasingly free to crack down on immigration without fear of alienating the business community.

Support for immigration has also waned as companies have moved to other countries. Since the early 1980s, U.S. manufacturers have increased their investments overseas more than eightfold, from $80 billion a year to more than $650 billion. And when companies move overseas, they stop lobbying for immigration at home. Why should a company fight to bring Chinese workers to the United States when it can simply move its factory to China?

Finally, companies have increasingly automated their production—and shed workers in the process. The U.S. steel industry, for example, produces as much steel today as it did in 1960, but with one-quarter of its former workforce. And most of the workers who remain are not the unskilled immigrants who once filled factory floors, but highly skilled workers—many of whom are native-born.

Of course, there are still industries like agriculture, construction, and hospitality that remain staunchly pro-immigration. In many ways, however, they are the exceptions that prove the rule. It’s impossible to pick strawberries, build skyscrapers, and clean hotel rooms from overseas, so these industries have continued to look to immigrants to provide cheap labor.

But even here, support for immigration is not what it used to be. Farmers in the Midwest who produce crops like corn, soybeans, and wheat were among the first to abandon their support for open immigration in the late nineteenth century, after new technology such as plows and combines enabled them to tend their fields with fewer workers. The mechanization of the cotton harvest in the 1950s and 1960s likewise led to the end of the Bracero Program, the agricultural guest-worker program between the United States and Mexico. And even among farmers who produce fruits and vegetables like tomatoes and strawberries, which largely need to be picked by hand, support for immigration has been declining, thanks to globalization. It is now easier and cheaper to produce and ship many of these goods from other countries, like Mexico.

Percentage of U.S. workers who are immigrants, by occupational group:

Farming: 46%

Grounds cleaning: 35%

Construction: 27%

Computer science: 25%

Food services: 22%

Health care: 20%

Source: Pew Research Center

These trends have meant that, today, the pro-immigration business coalition has lost its sway over the Republican Party. While tech firms—often the most vocal opponents of Donald Trump’s immigration policies—are relatively powerful, they tend to care only about the immigration of highly skilled workers, not low-skill laborers who represent the majority of immigrants coming to the United States.

As a result, even though nativist sentiment is declining in the American electorate overall, Republican politicians—from Trump to the Tea Party—are now free to play to their most xenophobic supporters. The reason the Republican Party is championing harsh immigration restrictions isn’t because nativists have somehow grown in stature. It’s because the business community has ceded the field to them.

Supporters of immigration must grapple with this new reality. Whereas appeals to the economic benefits of immigration may have swayed Republicans more than half a century ago, such arguments make little difference today. There are still opportunities for pro-immigration groups to engage the business community—working to craft an agricultural guest-worker program that supports farmers while providing better labor protections for workers, for example. But the vast majority of businesses that once supported immigration will not return.

The good news, however, is that support for immigration among the general public has surged over the past 20 years. According to the Pew Research Center, 59 percent of Americans say immigrants strengthen the country, compared to 33 percent who describe immigrants as a burden. When it comes to undocumented Dreamers, 73 percent of Americans agree that they should be allowed to remain in the country. That’s plenty of support to overcome the nativist sentiment within the GOP. Republican lawmakers need only do the math.