Homeland Security Secretary Markwayne Mullin’s proposal could block hubs like Boston, New York and Los Angeles from accepting international flights.

© Doug Mills/The New York Times

The methodically planned strategy is intended to pressure noncitizens, including many with legal status, to leave the United States.

© Salwan Georges for The New York Times

Clashes between protesters and armed federal agents have erupted at the parking lot of Delaney Hall in Newark since the Memorial Day weekend.

© Todd Heisler/The New York Times

But details remained scant after officials said last week that, with “extraordinary” exceptions, people seeking permanent residency must first leave the country.

© Valerie Plesch for The New York Times