It’d have to be a very prolonged 51% attack. Other nation states would likely join in, and it’s not like the USG can stop millions of people around the world from mining. Even if they succeeded in driving the price of most coins to zero, it’d be a Pyrrhic victory with USG looking like giant, insecure assholes spending a huge amount of resources just to destroy something that democratized money and banking. Months later, a new white paper would come out that finds a way to disadvantage state actors and viola, the game of whack-a-mole begins anew. People want out of dollars because the US economy is mismanaged, and that demand isn’t going away.