Building a wall
People seem to think it's just dandy for the Israelis to do that.
As for turning in "suspicious-looking" people: radicals come in all colors and shapes. It seems to me I remember a blue-eyed boy from California who was apprehended in Afghanistan with the Taliban fighters. McVeigh was blond. Could it be that some Mexicans realize that, as far as complexion, hair and eye color are concerned, the group on the border that most closely resembles Arabs is them? Could it be that, by promising to cooperate, they hope to defuse any mistaken-identity shootings based on color?