NEW ORLEANS—In drab, windowless rooms strung along a tight corridor, migrants who have flooded into the United States in recent years trickle before immigration judges each weekday morning.
These makeshift courtrooms are a far cry from the scorched border with Mexico and busy ports and airports through which these millions of immigrants have entered the U.S., almost all illegally. But despite the differences in miles, atmosphere, and often language, the people appearing in U.S. immigration court (“alien respondents,” in legal terms) know what is afoot.
In many cases,...