From the below video at 8:24,

Interior enforcement is the critical issue where the immigration service is concerned and the immigration system is concerned. I agree with Donald Trump about securing that Mexican border, but let me tell you, if we don't address the failings of interior enforcement, it doesn't matter what we do on the Mexican border.

I want to leave with a final image. Imagine sitting in a row boat in the middle of a lake and you find out that your boat has numerous holes in it. One of those holes is called the Mexican border. There are so many other holes that are being ignored. So even if you can plug that hole completely that says the Mexican border, how long will it take your row boat to wind up at the bottom of the lake?