For much of the summer, undocumented immigrants in the Los Angeles region had lived in fear of being swept up in federal immigration raids. Many rarely ventured out as masked, heavily armed agents arrested thousands of people as they went about their daily lives.

In recent weeks, however, a sense of normalcy had quietly returned after a judge in Los Angeles temporarily blocked what local officials and activists had described as random, indiscriminate raids.

Most of the National Guard troops and Marines whom President Trump had deployed to the city had been withdrawn, and the president seemed to have shifted his attention to other Democratic-led cities. Street vendors in Los Angeles returned to sidewalks, workers returned to construction sites, and families hosted birthday parties at local parks.

Now, immigrants, local officials and activists said, the nation’s highest court has ripped away that thin veil of safety. On Monday, the Supreme Court overturned the lower court order and allowed the Trump administration to resume immigration stops based on factors that include race or ethnicity, or speaking Spanish.

“We all thought the raids were over,” said Roberto Cordero, 67, an undocumented immigrant who lives in the Los Angeles area. “With this decision, we lost confidence in the courts.”