Keywords here: Illegal aliens. There's no immigration involved, they're simply here to cash in on hopping the border.
It is exactly the right thing to do even if the language which he uses isn't politically correct.
Do I actually think he will deport them all if elected? Of course, he won't. But he very well may put the onus on them to prove they are contributing to this country rather than the onus on the law to prove they should be deported.
"You can't deport everyone" is little more than code for "You can't deport anyone." You start with the worst offenders and deport them, then work your way down. A lot of them get the message and self-deport one you show we are serious about protecting our citizens and legal residents.