More than cut them off....prosecute them.
I think we will find though, the end of the money trail with these NGOs probably lands with China and other adversarial state actors who know full well the damage unchecked immigration is doing to us.
ahh you have already moved on to step 2
While I do not doubt that China, Russia, et al. have put some funds toward the invasion I think you will find that most of the Money comes from the US taxpayer laundered through a dizzying array of NGOs. One of the most difficult jobs any Republican president will have if they want to actually improve the country is to cut these funds off, as those who receive them will cry to a very receptive audience in the legacy press when you try to take away their rice bowl.