Obviously the police can ask almost any question, but what would have happened if the passenger told them, "It's none of your business what I'm reading," or even better, "I am exercising my right to remain silent."
Can the police legitimately take any action against you based on what they suspect you are reading or your refusal to answer questions on the topic?
I would think that would be a huge lawsuit, and the police would lose or be forced to settle - am I incorrect?
This makes me want to carry around some inflammatory/suspicious literature in hopes of provoking an incident.