Foday Turay first learnt he was not a US citizen as a teenager when he tried to apply for a driver’s licence. All of his memories were of America, so it never occurred to him that he did not have the paperwork to prove he had a legal right to be there.

“I went to elementary school here. I pledged allegiance to the flag. All I’ve known is the United States,” says Turay, who is a 28-year-old assistant district attorney in Philadelphia. “I don’t even remember anything about my birth country at all. I feel like an American more than anything in the world.”

Despite this, Turay and his wife are making plans for what should happen if he is deported to Sierra Leone, a country he left as a young child after his father was killed in a bloody, decade-long civil war. He has never been back to the West African nation.

Turay is one of the many millions of undocumented people who risk being swept up in Donald Trump’s immigration crackdown. The president-elect, who will be inaugurated on Jan 20, has promised mass deportations on a historic scale.

On his first day in office, the incoming president is expected to give federal immigration officers more powers to arrest people with no criminal records, end humanitarian programmes for migrants and start reconstructing the wall on the border with Mexico.

There will be “no price tag” on the cost of these efforts, Trump has said. Workplace raids, family separation and even trying to end birthright citizenship are among his expected measures. Legal immigration will also likely be restricted, experts say.

“Get ready to leave, because you’ll be going real fast,” Trump warned recent arrivals in an interview with Fox News. The incoming president told Time magazine he would do “whatever it takes to get them out” and go as far as legally possible.