I think Trump has a little bit of similarity to Hitler with the wall-building, people-evicting, muslim-banning stuff. You know "they're among us and we need to rid ourselves of them" is a pretty clear comparison.
If Trump implemented his deportation scheme, the end result would be a mega-surveillance state basically, and huge camps in which people are incarcerated for years on end: but women and children from every community in the USA would fill these camps, not terrorists. People would look back fondly on Guantanamo Bay as the quaint good old days.
Mexico is not actually a very big country, it would take decades for them to process deportation for 10 million people, and work out what to do with their kids, who are mostly American citizens, not Mexican citizens. There's basically no way to do what Trump says he will do without turning into Hitler and building huge concentration camps in the desert filled with women and children, taking about 5 million kids off their parents into foster care, or, to avoid the need for camps, truck entire families out to the desert then dumping them on the other side of the border.
But the bigger problem for ya'll is not what to do with those 16 million people, it's what police powers they'd need to get the 16 million people. I mean it's not like these people wear badges that say "I'm illegal". There are ~11 million undocumented immigrants, and about 5 million children to them who were born in the USA. That's about 5% of the entire country.
Trump needs a new agency with the power to dox everyone in the nation to find them. Who is going to man this agency. Probably guys who would like to be army or police or security guards but who aren't already hired for some reason (not a good sign). Then you're giving them excessive authority over a group of people which includes a large proportion of women and children. That's a recipe for abuse and corruption right there.
Of course, the new Immigration Gestapo won't just have authority over "illegals" they'll have authority over everyone. If you are stopped and don't have "papers" it's up to you to prove you're not an illegal immigrant, not up to them to prove that you are. 11% of the nation lack photo ID - twice as many as the illegals, and you could be stopped just walking to the shops and you forgot to bring ID. Your sister could be stopped by one of these guys, not have ID on her, then he's got the right to hold her in cells while he checks her immigration status. Just the threat of that is a recipe for intimidation and abuse.
So yeah, Trumps stated plan devolves into a Hitler-like mass surveillance system with rampant abuse where you're a suspect if you leave the house without your "papers" at any time - otherwise the plan just wouldn't work at all.