Trump is something of a last resort should Cruz and Kasich fail.
With the Donald, you've got to distinguish what he'd actually do from what he says. He's not stupid. He is not going to deport 11 million people, some of whom have American citizen children. Considering that what he's doing is (on paper, if not in practise) separating families from their children as a punishment, the court would probably rule it cruel and unusual.