Again, what exactly do you think Trump won?
Maybe you missed this part:
Mexico promises to deploy its National Guard throughout Mexico, particularly at the border, increase actions to dismantle human trafficking operations to smuggle individuals across the border, and take extra steps to coordinate with the American government to share information and "better protect and secure our common border," according to a statement from the State Department.
What Trump won was a reduction and quite possibly the elimination of migrants tracking their way to the United States. He won by having the Mexican government assist in this goal which helps our border patrol greatly. He won because he found away around the obstructionist Democrat led Congress who wouldn't lift a finger to stop the problems at the southern border.
There is no law that states asylum seekers must be hosted by the US government. They applied for asylum and now they can wait somewhere else.