At the moment I do not see the motivation to try to destroy bitcoin for a government. And even if they would try such a stunt, I doubt that mining all bitcoins is a reasonable strategy.
It's also impossible. The Us government could throw all their capacity at Bitcoin and either attack it or participate in it, but they cannot just mine all the remaining coins and hoard them. It would still take till about 2129 to mine all the coins no matter what they threw at it.