According to this article by Marielle Segarra for Marketplace, travel researchers Tourism Economics expect the number of international visitors to the USA to fall by 2 million in 2017, costing travel/tourism businesses $2.5B.
Tourism Economics President Adam Sacks is quoted as saying: "[Flight bookings, travel searches and other indicators] together are painting this picture of a shift in travel patterns away from the US."
Sacks also said that the strong US dollar is a factor, but the political environment - specifically President Donald Trump's "America-first" rhetoric - is a bigger issue.
Some potential visitors to the USA are said to be staying away as a protest against the Trump administration's proposed ban on visits from predominantly Muslim countries.
Sadly, the perceived safety of a destination is going to be a major factor in trip planning in 2017 (and subsequent years from now on, very likely). After terrorist attacks in Belgium and France in 2015-2016, London was high on the list of safe destinations. But that has suddenly changed. See the Related Listings (below) for more on recent trends re destination safety.