Now, I haven't read his book. But, I've been involved in many high stakes international negotiations. The anchor baby thing, and the military to the border thing...these are actions which are analogous to the types of gambits I might expect to see.
Non-citizens: "He can't do that, can he?"
- "Maybe he can."
- "Maybe we need to account for that possibility."
- "Maybe I won't go in the next caravan, until this gets figured out."
Voter: "Look at Trump. He's doing something! My man!"
Even if he presently intends not to do these two things, he nonetheless gets the type of behavior he wants by talking about doing these two things. And, he makes the other side look better when they finally come to the table and compromise with something that is far less radical than what he floated in the press. That is an artful deal, when the other side can claim victory with a "compromise" when the "compromise" was what you always wanted from the beginning (even though you said you wanted more).