The Fourth Amendment's guarantee against unreasonable searches and seizures has been regrettably whittled down over the years by the federal courts. Still, some meaningful protections contained in the amendment have managed to persist in U.S. law. As an example, consider a recent federal appellate court decision arising from the Trump administration's immigration crackdown in Los Angeles.
Last week, the U.S. Court of Appeals for the 9th Circuit largely affirmed a lower court ruling that found that the Trump administration was likely guilty of conducting illegal immigration raids in the greater Los Angeles area that violated the Fourth Amendment rights of multiple U.S. citizens.
Generally speaking, Fourth Amendment caselaw requires that an officer must have reasonable suspicion of criminal activity in order to stop someone. In the immigration context, a federal officer must have reasonable suspicion that a person is in violation of immigration law in order to detain them.
