With Congress deadlocked over how to handle illegal immigration, a growing number of towns and cities are taking matters into their own hands, using local laws to crack down on the problems associated with a massive underground population. In New Jersey, some towns have toughened traffic laws to deter contractors from picking up day laborers on city streets. Others have tried to ban workers from gathering on street corners to wait for work. Several have launched housing code crackdowns to combat overcrowding. One has banned illegal immigrants from renting apartments altogether. And few, are having much success. In a growing...