Start deploying the Army and Marine Corps along our southern border with their full battle gear.
They will look very weak when the people just walk by them....or totalitarian when they ‘stop’ and arrest women and children....
Won’t work...we lose the PR and the war.
Send as many troops to the border area as it takes to convince the Mexicans that we are ready to invade. Start blowing up the infrastructure in Mexico that leads to the border. The Mexicans will stop the caravans at that point. No body dies on purpose.