If America imposes a strict ban on the use of bitcoin like this, it will be bad news for bitcoin and most likely this will cause the price of bitcoin to collapse. I suspect that what the American government is doing is aimed at controlling the price of bitcoin.
If America becomes the next China, then BT will definitely face huge downtrends, but China did not accepted ETFs, and USA did, which means USA took the financial benefit from BTC by accepting it. Now they just have started so I don't think they will create a situation in which investors will suffer to live. As if investors won't be given proper facilities then they might even leave the country.
As, leaving the country can save them tax as well. Besides if USA citizens stop buying and selling BTC, it will still be functional. As BTC price is no doubt greatly influenced by USA but with time it will recover and the trend will shift to another country maybe.