* Smear campaign informing people its used for kiddie porn, drugs and terror.

* Telling people its actually devaluing their own currency! Those without BTC would instantly hate it.

* A ban on exchanges

* A ban on merchants accepting Bitcoin as payment.

I think these are much easier and cheaper than any form of network attack.
Its not out of the question... the US can do pretty much what they want when playing the 'terror' card.
I read that China already have legislation for virtual currencies?

I'm hoping this explodes Globally before any of this happens.