No, they can't. Generation speed is adjusted every 2016 blocks, up to 4x change. Let's say the NSA outcompetes the entire network by a factor of 400000%. This gets them about 8 weeks of bitcoins in a few days, before things are slowed back down to normal rates. Not nearly enough bitcoins to cause problems with.
That much power will let them mess around with what transactions get accepted, but that's an entirely separate issue. 51% attack is child's play at this point. What do you do against an adversary that publishes 500 different block chains designed to be easily confused with the 'correct' chain?
That much power will let them mess around with what transactions get accepted, but that's an entirely separate issue. 51% attack is child's play at this point. What do you do against an adversary that publishes 500 different block chains designed to be easily confused with the 'correct' chain?