It is unlikely that United States will ban bitcoin or other cryptocurrencies. The US Commodity Futures Trading Commission has already classified bitcoin as a commodity and is taxed by Internal Revenue Service as a property.
Although it is been under attack by some large US banks particularly the Bank of America for being a threat to their business, there is no way they can totally enforce a ban in the use of bitcoin. Cryptocurrency is a great idea for earning a profit and you can't stop an idea whose has time come.