[Sir Gawain]

My question is, what in the Constitution gives the Feds authority to prohibit farming of this crop, provided the state has approved it?

ROTFL. The government can do anything they damn well please. The Constitution is just for looks, until the citizens decide otherwise.

[Gabz]

The Constitution is just for looks, until the citizens decide otherwise.

The problem is that most citizens can't be bothered, and others like to use it to restrict people they don't like.