For a country like the USA, it's difficult, but in general, it’s not impossible if a country is willing, and El Salvador is living proof of that. However, I don’t think we should take his statement too seriously. Investors in the US are probably fine with Bitcoin’s current status. As long as they can use it and the government acknowledges it, they likely don’t expect it to become a legal currency like the USD.
Many people know Bitcoin is an ideal digital currency, but I feel that the world will oppose it a lot because it cannot have full control because of the decentralized system. Actually, I don't care too much about his statement because he doesn't support crypto.
Can it be a currency? I didn't think that far. But with the current conditions having had a huge space even the government benefiting from taxes, I think Bitcoin and crypto have shifted into a money industry. If the world government still believes in the centralized system, then the decentralized system will always be rejected because it will harm them.