Lol, good luck.
As some other, older, group might explain to you, deportations are hard and frigging expensive. You'd need beyond massive deportation centers and soon enough you'll need camps where you, I dunno, can concentrate people closer together, shall we say...
Even so, you need to transport these people somewhere, costing thousands of dollars per person. Twenty million people it was? That's 20-40 billion dollars. The camps themselves will go into the dozens of billions to build and maintain, adding all those prison camp guards, and removing roughly 5-10% of your workforce alone will wreck your economy.
If Trump deports as many people as he promised he would, it will wreck the US beyond recovery.
That leads me neatly into the next point: resistance. If you think you can deport 20 million people without anyone lifting a finger then you should read up on history. Also, now we have social media. It will be minutes until the internet overflows with horrible videos of innocent people getting brutalized or killed. That will totally not end up with mass protests throughout the country.
As soon as any of this starts it will become a shitshow like nobody has seen before, to use one of Trump's favorite phrases.
What more likely will happen in that a few tens of thousands people will be deported and that's it. Of course those deported likely won't be illegals, but who cares, they got Spanish sounding names, that's all they need. Republicans will start seeing the real cost of quickly abandon this stupidity and just act like mission accomplished!
Fuck it's hard to not be cynical, but if Trump / right wing Jesus lovers do what they want, they'll run the country off a cliff it will never be able to recover from. Not that I care at this point, let it burn. You will get what you voted for