This is a very good and important question. They probably could try, but they won’t. The government can outlaw anything it wants. It certainly tried in the past but historically it never succeeded with a prohibition of things people really want. They slowly come to terms that this is never a good idea.
Several other countries have already tried to block crypto usage (e.g. China, Turkey), and they are failing. In fact, the only thing they’ve seemed to achieve is push demand even higher.
But you also have to consider this: Very few cryptos are actually working to replace the US dollar as the world’s leading currency. The very best coins have real-life functions. They create ways to exchange critical data by allowing machines to talk to each other. They keep contracts honest and unchangeable. The government has no need to outlaw such useful things.
Sven Franssen