Our president says he will incarcerate and/or deport 2-3 million people immediately. Note that the current US prison population, while staggeringly high, is currently “only” 2.2 million, and our prisons are widely reported to be over crowded. So we’ll need a place to put the folks awaiting deportation, or being incarcerated.
It is my understanding that it costs about $10,000 to deport someone, and more to incarcerate them, bringing the cost of these deportations to at least $20 billion. He will probably want to find a way to bring the costs down.
On the other hand, Trump is probably not dumb enough to openly repeat a history that is universally derided by all parties and people.
So be on the lookout for a clever new euphemism for “internment camp” or “concentration camp.” Maybe this is how Arpaio fits in to the new administration.