“Go back where you came from” is an insult hurled at anyone in the United States who is considered foreign or out of place. That such an expression exists in a country that prides itself as a nation built on the hard work of immigrants is telling. Worse, those who say to someone “Go back where you came from” assume that people belong somewhere and have some place to return to.

The idea that undocumented people can be sent back “home” also underlies the U.S. Immigration and Custom Enforcement agency’s detention and deportation policy, as well as our immigration debate. But what happens when people have no home to return to?

As we know, many undocumented people were brought to the United States when they were little and grew up considering the U.S. home, but because their parents were undocumented, they too are undocumented. They might have arrived in the United States when they were a few months old and have no memory of their country of origin; their parents may no longer have family or friends there. But what we fail to discuss, or even acknowledge, is that they may be both undocumented and stateless.

Stateless persons have no formally recognized nationality or citizenship. They exist outside the realm of the nation state and have no legal or diplomatic protection from any nation. The U.N. High Commissioner for Refugees calls them “legal ghosts.” They have no travel documents. Their lives are on hold — sometimes for generations.

One of my students was born in Venezuela and grew up in the United States undocumented. He is a Deferred Action for Childhood Arrivals recipient. He is also stateless.

His parents fled the Hugo Chávez regime by escaping to Florida. As punishment for their betrayal, the Venezuelan government has refused to renew their passports — they have been rendered stateless for all practical purposes. If someone in his family gets sick or dies, they cannot return to help them or bury them. He is hoping the Trump administration will extend DACA and he will get to keep his temporary driver’s license and permission to work.

If DACA is not extended and ICE detains him, he will most likely end up in one of its infamous for-profit “immigrant detention facilities” in the Southwest, which leaves people and their dreams to rot, sometimes for years on end, or he will be deported to Venezuela. But as soon as the plane lands in Caracas, the Venezuelan government will turn him back, arguing he is not a citizen. He will be deported to nowhere.

According to the UNHCR, there were 65.3 million displaced people globally in 2015, and we know that number is only growing. Of these, approximately 21.3 million were refugees, 40.8 million were internally displaced persons, and 3.2 million were asylum seekers. According to the UNHCR report, of the 65.3 million displaced, it is estimated some 10 million are stateless, most of whom are refugees.

If we transpose these numbers to the 12 million undocumented persons residing in the United States (this number has held steady for the past eight years as immigration has slowed down and the symbolic “wall” has gone up), it can be estimated that hundreds of thousands if not millions of people here are not only undocumented but also stateless.

While “Dreamers” have caught the national imagination because they tend to be upwardly mobile students or successful professionals, their cause is easy to defend and dominates in the ultra-politicized landscape in Congress. But the DACA umbrella covers only 690,000 people. What will happen to more than 10 million undocumented and often stateless immigrants like my student?

Millions of people will continue to live in the shadows, living with the sword of deportation hanging over their heads, inhabiting a ghostly world, awaiting their passports to nowhere.