For decades, the United States tried to push undocumented people to self-deport, but success has often depended on coercion.

Residents have begun forming volunteer groups to monitor their neighborhoods for federal immigration agents. Others honk their horns or blow whistles when they see agents nearby.

© Jamie Kelter Davis for The New York Times

The Chinese Consulate in Manhattan has mobilized community groups to defeat candidates who don’t fall in line with the authoritarian state.