My understanding is that the US government cannot realistically regulate the Bitcoin protocol, but it can regulate it's own citizens use of it. It wouldn't be m

My understanding is that the US government cannot realistically regulate the Bitcoin protocol, but it can regulate it's own citizens use of it. It wouldn't be materially difficult to pass a law stating that all bitcoin transactions made by citizens and businesses subject to US jurisdiction must be registered. While they would not be able to block the transaction, they can go after anyone who made the transaction.