[tubbzor]

>So cannabis is illegal in the US under federal law, but not under state law in some states? Correct.

It all depends on who is attempting the search.

City/County/State entities have their respective jurisdiction and all must comply with state law, and therefore some states no longer have reasonable grounds to search based purely on cannabis scent. It would be equivalent to police coming to your house and smelling alcohol on your breathe and attempting a search based purely on that.

Federal entities, such as DEA and Dept of Justice maintain federal jurisdiction and can come in and trump state law (by definition). The Dept of Justice (Eric Holder specifically I believe) recently came out saying they would not prosecute those who are obeying state law as long as they don't sell to minors and keep it away from federal buildings/schools ect.