Just as the border wall and other border security measures are largely Security Theater, the coming "mass deportations" will be mostly a variant of that, call it Anti-Immigrant Theater. There's no way (ask any expert) logistically or economically it could ever work to really deport 20 million people, but the fascists will make a big show of looking like they're trying it, with very scary video of raids and detentions and loading people onto buses, etc etc. A lot of people will suffer and it will be a human rights atrocity but it won't really be what they are promising. Just like most election promises.