This is a really tough question, and the answer would likely depend on how many American investors have put their dough into Bitcoin. When stock markets crash, people run into safe havens, and this case the safe haven is the US dollar. They sell more speculative assets, in this case that would be stocks, and buy less speculative ones, in this case that would be major currencies and gold. Bitcoin is a highly speculative asset on its own, and investors may prefer to dump it too alongside stocks, but we can't say that with certainty.