We all know the US gov rules, dictate to rest of the world.
So if they cornered the btc market, afterwards the btc price could only go up, factor with this a few btc friendly directives, and a massive coup would have been achieved.
What is the downside?
They cannot do that unless they know who satoshi is, we're talking trillion dollars here means a huge amount of money will be at risk. Because Bitcoin is still young Investment method not even reached 20 years of history so if you really want to invest a huge amount of money to this kind of thing then investing a small amount will do.
But I think there are some US government Officials that already invest in bitcoin because they need to If they want to hide their assets and make it private to the other people.