I don't think he believes there is a mandate for amnesty --- it's just that whose interests are going to win out --- the Mexican elite could be quickly run out of power if immigration were slowed down in any way --- and our government doesn't want any big changes taking place with the power structure in Mexico. Right now, our leaders figure we have to keep them propped up --- no matter what the costs are to Americans.
Maybe, as someone posted earlier, we should offer them statehood.
Getting them under what's left of our constitutional government might not be a bad proposition to all.