Gov doesn’t to need buy all the hashrate.
They can do multi prong attack
drown the mempool with higher fees , they can spin more validation nodes , capture some miners etc …. And while they try this it will be tough to HODL
Discussion
Higher fees increase the motivation to bring more hashpower online, validation nodes don't do anything. But capturing miners is definitely something they will do during the hash war phase, assuming there are still miners in their jurisdiction.