I suspect a more effective method would be for Congress to pass a law that says you aren't allowed to use or trade high-energy-use cryptocurrencies. It would b

I suspect a more effective method would be for Congress to pass a law that says you aren't allowed to use or trade high-energy-use cryptocurrencies. It would be difficult to make the software unavailable, that cat's out of the bag and it runs into problems with free speech, compelled speech, etc. But the prevailing interpretation over the years of the Commerce Clause gives the Federal Government enormous constitutional power to do just about anything it wants when it comes to regulating anything that has any remote conceivable effect on interstate commerce. So I don't see what would stop them from saying you can't buy or sell goods with cryptocurrencies. They can make it illegal for any federally regulated bank (i.e. all banks) to get anywhere close to cryptocurrencies, such as accepting deposits from customers who traded crypto for cash, or providing banking services to companies that accept or trade in crypto. The Federal Government can withhold various federal monies from states that don't agree to implement similar restrictions domestically (that's how Congress can get around the "interstate commerce" part of the Commerce Clause--they can just bully states into complying with Congressional desires that the Constitution doesn't grant Congress the power to enact). Enforcement, of course, is another question. But if high-energy-cryptocurrencies are effectively declared illegal in the U.S., a majority of current users will likely not want to try to get around the legislation and that may be enough to shrink the market small enough to have the desired effect.