Martin Kaste is a correspondent on NPR's National Desk who covers law enforcement and privacy.

American police and local jails have traditionally refrained from immigration enforcement -- in contrast with police in many other developed nations. With the advent of President Trump's promise of "mass deportation," the feds are pressuring local law enforcement to help out. The result is a national patchwork of differing responses, political tension between sheriffs and police, red and blue states, and rank-and-file cops and chiefs. It raises fundamental questions about the sustainability of community policing ideals when they interfere with national policies about border security.