LoL.
The immigration issue is not an absolute deal-breaker in my opinion, because it’s not the biggest problem that the country now faces anyway.
I would rank the problems in this order:
1. Out of control spending long-term that will eventually bankrupt the nation and ruin the economy.
2. Slavish adherence to political correctness in all things, as one major example, climate change, preventing realistic and prudent solutions at the expense of fantasies of college professors with no actual clue.
3. National security; the Mexican illegal immigrants form a component of this but unvetted Middle East refugees are the larger component.
4. Unbalanced trade deals.
5. In this particular election, the prospect of electing somebody potentially worse than the current office holder.
6. Racial tensions that are being whipped up by cynical race baiters who need the unrest to remain relevant, and with a long-term view of social revolution (i.e. communism).
Some leeway is probably necessary on details of Trump’s plans to respond to any or all of these (no subtlety exists with point 5, you have to win the election to prevent this one).
As others have noted, finding, rounding up and deporting roughly ten to fifteen million people would not come easily or without costs, meanwhile if the trend can be reversed and policies enacted that will make the illegals think twice about staying, that will likely produce a good end result. Perhaps some will make good citizens after a process of returning and applying in good order.
For me, Trump would have to have a series of unprecedented reversals and meltdowns before he got even in sight of the failure barrier. He is so far ahead of the alternative in so many different ways that we should trust in the process and take whatever is available, at this point the choice is more or less get in the lifeboat or hang out with the captain on the bridge and see what happens after the hull cracks open.