first they will illegalize bitcoin using some funny excuses (drugs , laundering etc)
second ban bitcoin trading platform & frozen tons of bitcoin related companies' accounts (wall st damn banker are willing to do this)
third assert any bitcoin trading activities with US citizens is illegal ， prepare to suppress bitcoin companies overseas
fourth arrest tons of people to intimidate you guys
Yes, I should have said I'm focused on more "techinical" attacks like a 51% attack - things that could take it down worldwide. I think we have a good idea with precious metals how things would play out with the traditional "make it illegal" approach.