Assuming that bitcoin gets banned from the US it won't happen in a day or tow, people will have a notice before it does, and therefore i believe that between the time when the ban is announced and leading to the start of taking it into measure there will be a mayhem in the network , as all those coins and bitcoin that are owned by US resident start being moved, imagine how much bitcoin will be available to buy and that would mean that the supply will increase and that will actually affect the price in a bad way and we will see a high drop in it.