This would be possible by the FBI, or a federal agent of some sort, but state troopers are employed to patrol interstate highways, because they’re interstate, and sometimes to play a role in small rural towns that don’t have any local police, but only by agreement with the municipality.
Enforcement doesn’t just broaden itself to ruin your day. If a federal agent wanted to bust someone in a state where pot was legal, it would be a significant and newsworthy event. Other states where it was also legal would take notice, and hopefully their lawmakers would remind Congress of incongruities.
Marijuana is a federal offense, and the future of the law is anybody’s guess, but state troopers aren’t looking to change or violate the laws of their own state, and it’s not their job. If you break the law in your car on the highway you will get in trouble, according to the state’s laws.
So the answer is, he wouldn’t. But if he did, he wouldn’t be doing his job correctly, and that would probably be true in the eyes of the Attorney General of the state, to whom you could write a letter. The suspect would have a hard time back-peddling out of the problem, and may have incurred other perfectly legitimate charges.
For example, driving your car under the influence of marijuana is illegal in every state, and the suspect handed the trooper a good legal reason to suspect this, on a silver platter!
Especially if the suspect was holding pot in the glove compartment, driving, and even just a little argumentative or obstinate.
If this were to happen, I’d recommend not challenging the trooper’s decision on the side of the road, and getting a lawyer.
There are very few examples in the United States where federal authority ever overrides state autonomy, and for good reason.
It’s the foundation of a good system. And it’s historically endearing; in other words, they call it the “United States!”
But it comes to mind one unusual circumstance, that I’ll call the “bunny bazooka dilemma.” This is where your favorite bunny-rabbit hops across the state border, into your neighboring state, where hunting rabbits by bazooka is perfectly legal.
It’s lights out!
I’m making it funny, but this is the baseline of state authority, and the default way things are.
The rare situation is based on that innocent bunny not knowing the law (understandably), a little science, and preservation. If a federal wildlife refuge overlaps states, it could save your bunny and other wandering animals, wandering, but still part of wildlife, which is of interest to everyone.
You can probably see how a dispute between Alaska, for example, and the federal government over who can shoot the coyotes, in Alaska, on federal preservation land, can seem like a waste of time, compared to a solution through a single decision-making authority.
From a political point of view, or any other angle, things get awkward immediately without state autonomy. Generally speaking, if the federal government, tomorrow, said we’re going to enforce federal marijuana laws in Colorado, it would bring into question every instance, floating in the air, where the federal government is not interceding in state activity. States would protest.
The issue is bigger than the pot in your car.
From the point of view of you on the highway, on your way home from work, you’re under the state’s jurisdiction, directly.
If you are obeying the state’s laws, you’re safe from problems with law enforcement, unless you get pulled over by the FBI, which, it’s a long shot, but technically, could happen.
The bunny’s on his own! (In fact, I think it’s technically illegal for a bunny to smoke marijuana on a federal wildlife reservation!)
In the United States, people from all different states can support the concept of bunnies being under a safety umbrella that crosses state borders, but even with the cute edge, even with the bunnies hopping through the borders all day at their potential peril, it’s an example of very rare federal intervention, and it’s still controversial.
God bless you, and have a great day!