It seems that a few millions dollars thrown at some very powerful ASIC rigs could destabilise BC mining. What could prevent Bernanke from taking control of the BC mining with powerful computers? He's already throwing trillions at the monetary market. To take control of BC would be small change for the FED.
There is no incentive to disrupt Bitcoin. Barely anyone uses it, it's a hobby experiment currency of nerds and criminals, and in fact, the CIA would *love* it because they can use it to hide their illicit activities even easier (that's kind of why they sponsor Tor's development too!).
In short, it'd be done by individuals, not an organization (read: misguided politicians looking for support).