Any topic (writer’s choice)

Recently John and Sue, residing in Chicago, Illinois, vacationed in Denver, Colorado. During their vacation, they purchased some items of recreational marijuana, which is legal for use in both Colorado and Illinois. On their drive home along I-80 in Nebraska, they were stopped for an illegal lane change, and a search by a drug dog indicated the presence of drugs. They were arrested for the possession of an illegal controlled substance and jailed in the Cheyenne County, Nebraska, jail.

The federal government considers recreational marijuana illegal. However, they have allowed individual states to regulate the matter. Currently, several states have made marijuana legal for recreational use, while some others have recognized the use of medical marijuana (and more states will likely join these numbers).

For this assignment, assume that you are a defense attorney and represent John and Sue.

Discuss whether the mere interstate transportation of a legally purchased substance from one jurisdiction to another constitutes either a federal or a state crime when passing through a state which has not legalized the substance. 
In which jurisdiction would you want this case to take place, state or federal?  Explain why. Use case law to support your arguments.