The answer, researchers found, is quite a lot, both to taxpayers and the economy more broadly. Removing all 11.2 million undocumented immigrants, both forcibly and through Mitt Romney’s infamous “self-deportation” policy, would take about 20 years and cost the government between $400 billion and $600 billion. The impact on the economy would be even larger, according to the study: Real GDP would drop by nearly $1.6 trillion and the policy would shave 5.7 percent off economic growth. Researchers Laura Collins and Ben Gitis also write that their estimates are conservative, since they do not include, for example, the cost of constructing new courts, prisons, and other buildings that might be needed to process and detain millions of immigrants.

The study does not envision a new policy of mass deportation, with ICE agents rounding up immigrants in vans or going door-to-door to find them. Rather, researchers used the government’s own statement that it currently has the capacity to deport up to 400,000 immigrants annually (330,651 were removed in 2013) and asked what would happen if it actually did that, every year until the 11 million are gone. They also estimate that after the government announces a new policy of full enforcement, about 20 percent of the 11 million would leave voluntarily, leaving just about nine million that would need to be forcibly removed. “It still would be, I think, a shocking sight to the American people, to have the detentions, the deportations, the detention centers, the need for the administrative end of this,” said Douglas Holtz-Eakin, the group’s president. “If you were to do it faster and have vans sweeping in, I think that would have the untenable feel of the police state to the American people. We didn’t look at that.”