If financial institutions stopped allowing remittances—which they might do on their own, if Trump spooked them with a potential Patriot Act violation—the money wouldn’t stop. It would just be driven underground, into the hands of money launderers and other criminals, boosting the fortunes of the exact people Trump wants to build a wall against.
http://www.politico.com/agenda/story/2016/04/trumps-wall-plan-could-actually-increase-crime-000085
