In the months leading up to the 2024 election, Jill Garvey, an organizer in Chicago for liberal advocacy groups, gathered with some like-minded colleagues and, she recalled, “did some scenario planning.”

“Our sense,” she said, was that “authoritarian movements had coalesced, had singular goals, and were advancing them.”

Since then, the organization that Ms. Garvey founded shortly before Election Day, States at the Core, has hosted regular Zoom trainings in how to track and document the actions of federal immigration agents. These seminars on “ICE-watching” — referring to Immigration and Customs Enforcement — now draw thousands of attendees at a time.

ICE-watching has been at the heart of the opposition to the Trump administration’s raids in Minneapolis, where activists’ unrelenting pursuit of often-bellicose federal agents has led to frequent street confrontations. In two such incidents, federal officers fatally shot Renee Good and Alex Pretti, both Minneapolis residents, killings that were captured on camera from multiple angles by observers.

The videos of these shootings and other instances of aggression by immigration officers have succeeded in doing what perhaps no other anti-Trump protest has done: draw concessions from the administration.

On Wednesday, Tom Homan, Mr. Trump’s border czar, announced the withdrawal of 700 federal agents from the city, a move that followed the reassignment of Gregory Bovino, the border patrol official who had served as the face of the Minneapolis operation.