If I were Trump, on my first day in office I would contact the Mexican president, and I would tell that president this - "Those migrants down on your border, you will send buses to pick them up and carry them to shelters within your interior". You will evaluate them, and make a report on who they are, and what is the reason they were attempting to flee your country or cross through your country on their way to the American border. You will give them safe haven from the elements for safety. We will assist you in helping those in need, but we will not be doing so as a gesture that says we will be taking them in, but we will help you to figure out what their problem is if need be. Now, if you don't do what we say, then very severe sanctions and tariffs will be implemented immediately.