Trump sent a legal immigrant to a hellish Salvadoran prison by mistake. Why won't the U.S. bring him back?

“How can I be under arrest? And in this manner?” Franz Kafka’s famous fictional character, Josef K, asks the two men who show up at his apartment early one morning. 

“We don’t answer such questions,” the men tell him.

“You’re going to have to answer them,” K responds. “Here are my papers, now show me yours, starting with the arrest warrant.”