I don't understand why you are obsessed with not calling it a currency. You haven't showed us any of the laws you claim would make a non-backed currency illegal, and bitcoins are being used as a currency, so I don't see any reason to not call it a currency.
So on what grounds will a Senator be able to shut it down?
With legislation maybe like China did a few years ago with "Virtual Currency"? But can you do that to unique digital goods/commodity that has ownership and is transferable in a free market system?
Some might say its untraceable? - Only if you launder it - that's illegal - not if you trade/barter a digital good/commodity?