Under the border search exception, federal officers may generally conduct routine, warrantless searches of persons and items entering the United States without reasonable suspicion or probable cause of unlawful activity. However, stops and searches conducted in areas farther from the border may require at least heightened suspicion or probable cause of unlawful activity to withstand Fourth Amendment scrutiny.
constitution.congress.gov/…/ALDE_00000239/
They can do warrantless searches. Just not within the entire 100 mile border. A fair distinction, but they definitely can at the border and ports of entry, and do so routinely.