Yet President Trump has betrayed the loyalty of Afghan refugees by conducting a mass crackdown against them. Shortly after taking office, he called into question the legal right for many of them to be in the United States. Now, in response to the Nov. 26 shooting of two National Guard members, Mr. Trump has gone even further. His administration has prevented the admission of Afghans still trying to find safety here. It has cut off support services for Afghan immigrants who have made it here and has detained some people for more than a month without charges. Stephen Miller, a top Trump official, has threatened to deport refugees who came here legally.