It's a States Rights issue. Different States have different laws.


Forth ammendment of the US Constitution

The right of the people to be secure in their persons, houses, papers, and
effects, against unreasonable searches and seizures, shall not be violated,
and no warrants shall issue, but upon probable cause, supported by oath or
affirmation, and particularly describing the place to be searched, and the
persons or things to be seized.

I don't know about the Feds and their Patriot Act, but state and municiple
authorities cannot search your vehicle without probably cause. Agreed,
probable cause can be a slippery slope, but they do not have the right to
search every vehicle at their own will.