When the Border Patrol is at the non entry border points receiving the border crossers or capturing them for processing they are aiding in the illegal migration to the US. The Border Patrol either holds them for their court date or releases them into the US interior.

Obviously those that trek to the US border to cross at non entry points know this.

You can see why the increase in border crossings with the current law that is to be followed.

Trump is trying catch and hold but does not have the housing facilities to hold this enormous amount of border crossers.

A border barrier at the most easily crossing points along the border is the best option.