Imagine the population of Chicago. Then quadruple it. That’s about how many unauthorized immigrants Donald Trump hopes to remove from the country: 11 million people in all.

It won’t be easy. How will the government find all of these people? Where will they be held as officials process their cases? Will migrants’ home countries take them back? And will lawmakers approve all the funding required for this?

The Morning is running a series on the policies that Trump and his congressional allies will try to implement next year. Today’s installment will look at his mass deportation goals.

We already know the broad contours of Trump’s plan. He wants to use the military and law enforcement to detain the millions of people who are in the United States illegally. The government will hold them in detention facilities while it inspects the facts of each case. Finally, it will fly undocumented migrants to their home countries or other places that agree to take them.

We know less about more specific details. Here are six lingering questions:

1. Who are the targets? Trump aides say they will prioritize migrants with criminal records and previous removal orders, who number in the hundreds of thousands. The federal government already knows where to find most of these people, thanks to their previous contact with law enforcement, and can quickly deport many.

The question is who comes next. Trump also wants to deport undocumented migrants with clean records (aside from the blemish of breaking the law to enter the United States). And he has said he’ll go after people with Temporary Protected Status, a program that allows some migrants from specific countries to stay in the United States legally. These migrants could be harder to find and detain, especially in cities and states that call themselves sanctuaries for the undocumented. Those places have refused to cooperate with most federal deportation efforts.