Similarly, the U.S. Government could easily create a pool of mining supercomputers worth millions of dollars, and easily take control of the network as well.
I don't think that the US government is very likely to do that, since the bitcoin doesn't yet possess a danger to the US dollar when it comes to daily payments, but also international transfers and it won't "steal" the dollar's position for a long time. It's for a very simple reason; there are still a lot of people whose mentality wouldn't make paying with a currency which doesn't exist IRL logical. Bitcoins are therefore very unlikely to be attacked by a government of any country, unless the things I named above change.