The actual fighting is a military responsibility, certainly. The problem is that Washington will not admit this is happening. Nor will the MSM. Time for citizens to go out and bring back evidence of incursions to media sources that will listen: Drudge, et. al.
One potential source of hard information on this could be...amateur astronomers! They go out into the Arizona desert, to border sites like Vekol Valley, Sentinel, and Organ Pipe, armed with sophisticated camera gear and portable telescopes, looking for the darkest places. Now are dark-sky border places not the very routes illegals might also favor?
Intelligence is found in unexpected places.
"The problem is that Washington will not admit this is happening. Nor will the MSM."
I don't know how bad it must get before action is taken.
I wish US well.