CHAMBLEE, Ga. — Not many notice when the SUVs arrive. Around 5 a.m., when the immigration agents pull into the parking lot of the Chamblee Heights apartments, 16 miles from downtown Atlanta, only one person is on the lookout. Cristina Monteros catches sight of the cars with the telltale tinted windows from her small apartment near the front, where she runs a day care, and calls her downstairs neighbor: ICE is here. The neighbor dials another, who passes it on. It takes less than 15 minutes for everyone in the complex to hear about “la migra,” whereupon they shut their...