Last week a group of Missouri prosecutors announced it had taken legal steps to block voter consideration of a medical marijuana proposition on the November ballot.

In a news release, the group said it opposes the measure because pot is illegal under federal law. "Missouri law cannot usurp federal law," the prosecutors claim.

That doesn't seem to have been a problem in Colorado, where recreational marijuana is sold, but let's leave that aside for the moment. Instead, let's focus on the prosecutors' central argument: state law, they say, must give way to federal law whenever there's a conflict.

[continues 383 words]