Buying ASICs is easy, but a government wanting to destroy Bitcoin means turning against its citizens. The "Bitcoin is used for illicit activity" excuse card means accusing every citizen of sustaining illicit activity. Not a good idea.

But let's hypothetically say they did really want to destroy it. A 51% attack is possible, damage could be done but it could also be reversed by reversing blocks. 51% attack means they have to own 51% of the mining power, so they either do it by slowly adding more and more ASICs into their system to slowly rise the hashrate during a longer term or they would plug all of them in at once and there will be a 110% hashrate spike.

About being noticed, I'm sure there will be lots of people and articles everywhere on the Internet posting screenshots of the hashrate spike. Twitter would be full of them.

Am I missing something? I've never been deep in Bitcoin mining before so this post might contain stupid statements and any correction is appreciated.

EDIT:


It won't? Where would it be allocated then? I thought the hashrate charts represented the total Bitcoin mining hashrate.