Key dates in recent history:
Trump Slump Means U.S. Tourism Is Losing Visitors From Its Most Important Markets. (Skift, 11/30/2017)
This slump began in late 2016 — the first year that notched fewer international arrivals than the previous year since before the global recession of 2008 — and continued into the early months of 2017.
It coincides with the election of President Trump in November 2016, although it’s not clear how much of the decline this year can be attributed to the political uncertainty. [Yet it's still called the "Trump slump".] Headlines about travel bans and building a border wall, however, as well as an actual tightening of visas for refugees, certainly played a role and didn’t portray the United States as an inviting place to vacation.