Donald Trump has promised voters that he would carry out a range of immigration actions, including deporting, with the help of the National Guard or military, millions of immigrants living illegally in the U.S.

Many of Trump’s plans do not require congressional approval, but they still might be hard to undertake at a scale that Trump has described.

Amy Lieberman, a politics editor at The Conversation U.S., asked University of Southern California immigration law scholar Jean Lantz Reisz to explain how Trump could follow through on some of his immigration promises during his second administration – and what legal and political obstacles he could encounter along the way.

What role do states play in any Trump order to deport immigrants?

There are 11 million people living without legal authorization in the U.S., and Trump would have the authority, as president, to deport those people. But it would be very expensive to pay for the immigration officers, immigration judges, detention facilities, the plane flights and more that would be required to do so. Estimates on the cost of mass deportation range from US$88 billion a year to more than $300 billion.

The administration is probably going to have to rely on state and local governments to help carry out these deportations. The president cannot legally force state and local governments to cooperate with immigration enforcement. About 10 states, including New York, Massachusetts and California, have laws that prohibit cooperation with Immigration and Customs Enforcement, or ICE – the federal agency that oversees immigration and deportation – under certain circumstances.

For example, in California, employers may not allow ICE to enter nonpublic areas of their workplace........

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