Answer: Probable cause is what is required to search a motor vehicle to see if the vehicle contains drugs or contraband. That usually means that a standard of guilt is more than a mere possibility. If the police fail to get a warrant, they oftentimes try to justify searches on a probable cause theory. Previously, they also tried to justify searches because it was incident to an arrest. However, the case of The United States v. Gant from the United States Supreme Court has held that automatically searching arrestees’ vehicles is impermissible under the Fourth Amendment to the Constitution. I do have an article that I wrote analyzing such searches for the Wisconsin Law Journal elsewhere on our website.