President-elect Donald Trump has vowed to launch a mass deportation program starting on day one of his second term. That could have devastating consequences for the millions of people residing in “mixed status” households: those in which both undocumented immigrants and people with permanent legal status reside.

Trump has said that he would rely on an 18th-century law to carry out mass deportations and that he intends to first target “known or suspected gang members, drug dealers, or cartel members.” Vice President-elect JD Vance has set an initial goal of 1 million deportations. A representative for the Trump transition team did not respond to a request for comment about whether any exceptions would be made for undocumented immigrants who have lived in the US for a long time or who have immediate family here, including US-citizen spouses and children.

There are many such people: The US has an estimated 4.7 million mixed-status households, according to a 2024 Center for Migration Studies report. Roughly 500,000 people in those households may have hoped for new protections against deportation through a Biden administration program that would have cleared the way for undocumented spouses and stepchildren of US citizens to apply for legal status. That program was struck down in federal court on Thursday.

If Trump gets his way, his deportation program threatens to rip families apart in what could be a new iteration of his first administration’s policy of separating immigrant families. However, Tom Homan, Trump’s former director of US Immigration and Customs Enforcement (ICE) and current immigration adviser, has also proposed that families could be deported together, apparently including US citizens. It is not clear whether he was suggesting that they would go voluntarily together.

There are clear practical challenges associated with implementing a mass deportation program on the scale Trump is promising. But if he manages to overcome those hurdles, such a program could wreak lasting psychological damage on millions of American-born children in mixed-status families, place economic strain on their communities, and even weaken the US economy.

The familiar damage of family separation

Research on the effects of Trump’s previous policy of separating immigrant families sheds light on the potential fallout from breaking up mixed-status families through mass deportations.

In his first term, Trump adopted what was called the “zero tolerance policy” for undocumented immigrants arriving at the southern border. Parents were sent to immigration detention to await deportation proceedings. Their children, meanwhile, were sent to separate facilities operated by the Department of Health and Human Services and, in some cases, released to other family members in the US or to foster homes. (Previous administrations, in most cases, would not have detained the parents or children, releasing them together into the US.)

At least 5,000 families were separated before a California federal court ordered the federal government in June 2018 to reunify the families affected and end the policy. As of May 2024, some 1,400 still had not been reunited, despite an ongoing Biden administration effort to do so.

The harm the policy would inflict was well-known to Trump officials at the outset. Commander Jonathan White, who previously oversaw the government’s program providing care to unaccompanied immigrant children during the first Trump administration, told Congress that he had repeatedly warned the officials who concocted the policy that it would likely cause “significant potential for traumatic psychological injury to the child.”

A September 2019 government report confirmed those effects, finding that immigrant children who entered government custody in 2018 frequently experienced “intense trauma,” and those who were “unexpectedly separated from a parent” even more so. In 2021, a group of pediatricians concluded in a study that separating families “constitutes cruel, inhuman, or degrading treatment that rises to the level of torture.”

As Vox previously reported, psychologists have seen that childhood trauma manifested in three main ways: disruptions to social attachments, increases in emotional vulnerability, and, in some cases, post-traumatic stress disorder. Those symptoms could be short-lived or they could persist; they could also not even manifest until a child enters their teen years or adulthood. Any of them could significantly hinder a child’s later success in academics and in the workplace.

The family separation caused by mass deportations would look different from family separation at the border, and whether the psychological effects on separated children are more or less extreme will depend on their circumstances. What is clear, however, is that mass deportation would cause family separation at a scale far larger than anything Trump tried in his first term in office.

“This is orders of magnitude higher as far as families that are going to be split apart, and the kind of life-altering consequences of that will be visited upon 5.5 million US-born children,” said Matthew Lisiecki, a senior research and policy analyst at the Center for Migration Studies.

He and his co-researcher Gerard Apruzzese conservatively estimate that a third of American-born children in mixed-status families, including 1.8 million who live in households with two undocumented parents, would remain in the US even if their household members were deported.

That would inflict not just psychological suffering, but also a hefty financial cost: Children who remain in the US would see their median household income drop by nearly half, from $75,500 to $39,000, if their undocumented household members were deported, Lisiecki and Apruzzese found. Other family members or public social services would have to pick up the cost of raising them, which the researchers estimate at $116.5 billion. The loss of their parents’ productivity — and the $96.7 billion they contribute annually in taxes — could also hurt the US economy.

“The kind of trauma experienced as part of that is something that these Americans will be living with every day of their life from here on out,” Lisiecki said. “I don’t think we have the experience at that scale to say what that means for the lives of those kids as they grow up and move forward.”

Whether Trump can actually deliver on his promises of mass deportations is a big question mark. He has said that the program would have “no price tag,” suggesting that the budget is unlimited, but he would need the support of Congress to make that happen. It’s not yet clear that he’ll have the numbers to increase the immigration enforcement budget, especially given that control of the House is still undecided. But even if implemented on a small scale, the consequences for affected mixed-status families would be dire.