Customs officers have full powers under Title 19 Section 1581:
“Any officer of the customs may at any time go on board of any vessel or vehicle at any place in the United States or within the customs water of, as he may be authorized, within a customs-enforcement area established under the Anti-Smuggling Act, or at any other authorized place, without as well as within his district, and examine the manifest and other documents and papers and examine, inspect and search the vessel or vehicle and every part thereof and any person, trunk, package, or cargo on board, and to this end may hail and stop such vessel or vehicle, and use all necessary force to compel compliance.”
Anyone who fails to realize that this legalizes all sorts of abuse and misuse is an unmitigated moron, and I'm ashamed to call them my fellow Americans. This is far too broad a power for any government agent of any level.
"Since someone, somewhere might want to do something bad someday, we can do whatever we want to anyone, at any time, without cause or justification, and without limit" is the excuse used by every tyrant ever. It has no place in a Just Nation.