Even if, and that is a BIG 'if' they were to try to do as you say they would fail miserably (something they are getting good at) due to the decentralized nature of how bitcoin works. And if they interfere to the point it becomes a major hassle an alternative will be invented, such is the nature of technology as alluded to in the senators statement. Every force ('action') on one object is accompanied by a 'reaction' on another, of equal magnitude but opposite direction. In other words they push, we push until the money runs out and the US government is broke and on its knees right now. They cannot sustain the level of coercive and direct action that they have been for much longer and I truly believe change is coming and coming soon. They cannot contain and control everything and the tighter they try to hold on the more it pushes through their fingers like sand. I can only hope there comes a point when common sense and rationality prevails and all this nonsense with prohibition and the justice system is brought to an end.