This directive is immaterial to the illegals who come in at the southern border. It is directed towards legals who enter, and US citizens who leave and reenter. If you will remember, the 19 Arabs of 9/11 were here LEGALLY. The Portland and Buffalo (Lackawana) cells were US citizens. Jose Padilla and John Walker Lindh were US citizens. Richard Reid was a Brit on a valid UK passport.
The southern border needs better control, but that has nothing to do with this.