Donald Trump’s inauguration is just weeks away, and with it comes the promise that the new president will try to quickly deliver on one of his most troubling and damaging priorities: the mass deportation of millions of undocumented immigrants.

If it goes ahead, the development will undermine the government’s economic goals, cut budgets and red tape, and destroy families. The president-elect has said that immigrants are “poisoning the blood of the country,” calling them criminals, animals, invaders and worse. But undocumented immigrants have a long tenure in the U.S. and are the lifeblood of key occupations and industries — raising the question of how mass deportation became the centerpiece of the incoming administration’s agenda.

This position is not so new. The US has been carrying out large-scale deportations for decades. Congress and successive administrations have invested huge sums in enforcement of deportations, increasing ninefold since 2002. But Trump’s critics insist his plan will require “massive” additional investment.

Trump’s last term in the White House had fewer annual immigration deportations than previous administrations. In his second term he has pledged to deport a million people a year and seal the US-Mexico border. Neither will happen, but the plan will have serious consequences for immigrants.

Many will try to avoid accessing public services. They will not report crimes or cooperate with investigations for fear of deportation. There will be an increase in hate crimes against immigrants. Proposals like Senate Bill 72 in Missouri, which would pay state residents to find and take into custody their illegal neighbors, will proliferate. Even with all these unfavorable conditions against them, it is unlikely that large numbers will voluntarily leave, as the incoming administration is urging. Most of the illegal immigrants have built their lives in the US and believe that their children, who are US citizens, will have a better future here than in their home countries. So they will do what immigrants have always done and try to deal with it.

Trump continues to defend his plans through a mix of bogus propositions that won’t survive legal challenges. It has inflated the number of undocumented immigrants to 15-20 million and maximized the threat they pose. There are about 11.7 million undocumented people in the U.S., slightly below the all-time high of 12 million in 2008.

His plans will actually increase the number of undocumented immigrants because he also wants to remove residency status from groups who have been granted temporary residency in the U.S. on humanitarian grounds, about 2.5 million people. Immigrants from Venezuela, Nicaragua, Haiti and others will be forced to return to the dangerous countries they fled. Tom Homan, Trump’s nominee for “border czar,” supports deporting children who are American citizens but whose parents are undocumented. Children in many affected families, however, will remain in the US with a second parent or legal guardian, or will be placed in foster care.

The new administration will likely roll back the high fees, bureaucratic barriers and regulatory requirements implemented during Trump’s last term, making it much more difficult for immigrants to gain legal status and permanent residency, further swelling the undocumented population.

Most of the illegal immigrants cannot or should not be deported. Many are trapped, for example, in the immigration system where there are 3.6 million pending cases and 4.1 million unapproved visa applications. Some people fall into both categories.

The best way to deal with these groups would be to wait for their affairs to be settled. The best way to fix the underlying problem would be to reform the visa system and invest in immigration courts and asylum judges.

The Posse Comitatus Act of 1878 prohibits military personnel from participating in civilian law enforcement. However, Trump has argued that he can deploy the military to remove immigrants because “they are not civilians, they are invaders, the likes of which no country has probably seen before” (tell that to the Ukrainians). He vows to “save every invaded and conquered city” (of which there are none).

Trump’s proposal to deny citizenship to the US-born children of undocumented immigrants would apply the logic of the infamous Dred Scott decision. It would violate the 14th Amendment and transform a country renowned for its historical genius at integrating immigrants into one with a hereditary subclass of “illegal” persons.

Trump has pledged to deport convicted criminals. However, these groups have been the priority for deportation of all recent administrations, with the exception of the first Trump administration, which set so many priorities it was practically as if none were set. Additionally, programs and systems have long been in place to remove individuals after serving prison sentences. The same applies to those ordered removed by an immigration judge. However, Immigration and Customs Enforcement, for a variety of reasons, has failed to execute 1.4 million pending removal orders.

Trump’s case for mass deportations also rests on the inaccurate claim that most immigrants entered the country “uncontrolled.” Instead, most people who crossed the border presented themselves to border agents, and most of the irregulars in recent years entered legally on temporary visas.

Some immigrants voted for Trump, believing he would improve the economy and deport criminals. However, if the past is any example, the second Trump administration will treat all undocumented immigrants and their children as criminals. This means that 4.8% of the US workforce will be outsourced. Three-quarters of undocumented immigrants are considered “essential workers,” compared to 65% of natives. Immigrants also work in more dangerous industries and occupations than natives, as indicated by injury and fatality rates. The agriculture, construction and health industries will be particularly affected. Workers will disappear, consumer costs will rise and businesses – large and small – will fail.

There is an alternative. Since 1929, the US has offered legalization (called a “registry”) for undocumented residents of good moral character, recognizing that otherwise deserving immigrants are trapped in the legal immigration system. In the first decades of this law, Congress reduced the length of stay required. However, to qualify today, an undocumented immigrant must have entered the US more than half a century ago. A bill that would change the entry date to January 1, 2010, would cover the 79 percent of the U.S. population that is undocumented and reduce the pressure on federal immigration agencies.

If Trump is serious about solving immigration challenges, he should adopt a registry program, provide strong funding for immigration courts, and reform the visa process. All of these actions would do much more to create a successful and safe immigration system than a harsh mass deportation program.

Donald Kerwin is the editor of the Journal on Migration and Human Security. He is the former executive director of the New York Center for Migration Studies and a former senior fellow at the University of Notre Dame’s Keough School of Global Affairs.