Markets are at limit down circuit breakers again after open. This reaction is less about the travel ban, and more about the confusion of the announcement. Commander in Chief got on national tv and said 'ban all travel to Europe'. The paper signed doesn't say that, it says, ban incoming folks from Europe who are not Americans.
Fear in the markets, and public in general, right now, is driven by the confusion and incoherence in the messaging more than the message itself. Everybody realizes 'something bad is happening'. But the real scary part is, those driving the bus seem confused about where it's going and there isn't a consistent message from leadership. When C&C goes on tv to make an announcement, then gets it wrong, that does more harm than the announcement itself.