1. Introduce FedCoin - a compatible fork of Bitcoin pegged to the US dollar by the Fed.
2. Ban all US companies and citizens from buying, selling, exchanging, or trading in, alternative cryptocurrencies (such as Bitcoin).
3. Set the initial Fedcoin difficulty lower or comparable to Bitcoin, but peg the initial price higher in USD (the Fed can do this because they can print unlimited dollars).
4. Watch as every Bitcoin mining operation on the planet leaves Bitcoin in droves to mine FedCoin.
5. Watch as all but the diehard US holders of Bitcoin sell, causing the price to crash (further disincentivizing miners)
This isn't entirely dissimilar to how the US destroyed the Gold market to hoover up all the Gold in the early 20th century.
Now I don't think this is going to happen just because enough people in government own BTC at this point, but it's not impossible. And it has nothing to do with the resilience of the computing network. You could mine Bitcoin over TOR or I2P to keep the network alive but it won't matter.
To kill Bitcoin entirely the Fed would likely have to convince the FedCoin miners to periodically launch 51% attacks against the Bitcoin blockchain.
You can imagine someone burying at the beginning on iron age (which happened less than 5000 years ago) big chunk of this wondrous, rare and hard to work with material. And today we are making insanely huge buildings out of it.
You can eat them. If you salt them, they'll last a long while.
If one day I came up with a nuclear reactor that turned rocks into gold, maybe the market might drop the price of gold, and it would collapse just the same. And it will happen, just probably not in our lifetime.