When can police search your car?:
While police generally need a warrant to search you or your property - during a traffic stop, police only need probable cause to legally search your vehicle. Probable cause means police must have some facts or evidence to believe you're involved in criminal activity. Ref. Source 4
This will lead to a question about how they determine if you are a criminal or not. Many African Americans and Hispanics cry foul at being targeted for a search because of race.
International Level: Politics 101 / Political Participation: 3 0.3%