I don't think that the US would be worried about Bitcoin that much, since Bitcoin is not as stable as the United States Dollar is. I believe this is just an excuse from the government to begin cracking down on Bitcoin and crypto as we know them. After all, they're convinced that Bitcoin and other cryptocurrencies are used for money laundering and tax evasion. While we all know that criminals use Fiat more thoroughly for this than Bitcoin or any other cryptocurrency, the US government doesn't care. All it wants is to have supremacy over the world with the United States Dollar as its reserve currency. The US is a "little afraid" that Bitcoin could take down on the existent financial system as we know it.
The truth is that Fiat is (and will always be) in the lead of our economic system because it's backed by the full faith and credit of the government. Since Bitcoin and other cryptocurrencies don't rely on a central authority, they're "less trusted" among everyday people. The USD will continue to reign supreme until another Fiat currency takes its place sometime in the future (which I doubt it will ever happen). The recent popularity of crypto and Blockchain technology will pave the way for government-issued digital currencies within the mainstream world. The US and other countries will have no choice but to transition from physical cash to digital cash in the future, in order to prevent crypto from "replacing" the world's economic system as we know it.
In the end, I believe that the US will launch its digital version of the USD while other countries will follow. Bitcoin will still remain alive as an alternative to Fiat, but its prominence will not be that much within the mainstream world because of the emergence of government-issued digital currencies. At least, people will still have a decentralized financial system to use. But in no way, decentralized cryptocurrencies like Bitcoin or Ethereum will replace government-issued currencies. The US and other countries might try to shut down Bitcoin and other cryptocurrencies but they'll be unable to do so because of their decentralization/censorship-resistance. Both digital Fiat and crypto will live in harmony for many generations. Just my thoughts