What they probably WILL do is shut down the wire transfers into US bank accounts from banks dealing with bitcoin. For example, due to federal banking rules, Mt Gox really hinders the movement of dollars through their exchange.
If Bitcoin grows, you will see the Treasury jump ugly over it.
But then that leaves the rest of the world and only 12 million Bitcoins at present. Doesn't take many owning only 1 to suck up that miniscule inventory - only about two thirds of the people living in Hong Kong.
We shall see... Watch who in the senate comes out against it - then you'll know more of what to expect. It might actually be better for our "leaders" to ignore the owners of the Fed, embrace it and tax it to death instead... lol
Oops, I got that wong. I was thinking about the population of Mexico city. lol There are only about 7 million living in HK. ;)