Former President Donald Trump faces steep challenges to carrying out the largest deportation operation in American history, as logistics, cost, and political considerations could get in the way of removing illegal immigrants en masse.

Trump has remained light on details when it comes to how many noncitizens he would deport if he wins a second term in office. His campaign has only said it would begin with “the nearly 500,000 convicted criminals who Kamala Harris has allowed to remain in the country.”