When President Donald Trump expanded federal operations in Washington, DC, nearly 30 days ago under a “crime emergency,” residents swiftly began recording arrests of suspected undocumented immigrants on their phones and warning others of traffic checkpoints through apps like Instagram. These are techniques that community patrol groups in Los Angeles have been using for months: A wide range of messaging services, tech tools and social media sites have been enlisted to track immigration enforcement activity in Southern California. For immigrant neighborhoods, these platforms have become vital news sources and alert systems.

Citizen monitoring is likely to grow as Trump ramps up his immigration crackdown in other cities. But while recording police and other public officials is protected by the US Constitution, experts worry about the limitations of those protections, as the administration has said that filming or documenting agents at work threatens their safety. The line between observing federal activity and obstructing agents — which is a crime — is murky, contributor Patrick Sisson reports. Today on CityLab: As Immigration Crackdown Expands, Citizen Activists Observe and Report

— Linda Poon

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