Hardly surprising given that international travel, especially for leisure is exceedingly sensitive to perception of the news. It takes a long time to build up tourist numbers, but a small incident can cause the sharpest falls immediately.
But I'd argue that even before the Trump administration, the USA was immensely difficult to travel to for anyone in a country that's not part of their visa waiver program. USA is one of the few places to require a transit visa even if you only connect at one of their airports and visa arrangements have exorbitant fees attached to them. They have a perception abroad of having stressful border control - even so for Canadians who arguably enjoy the easiest access to the US compared to any other country.
It certainly doesn't help to have higher minimum salaries for work visas and a possibility of being kicked out after completing a degree on study permits, which affect business and student visitors respectively. And finally, dealing with American companies from abroad can be a huge resource commitment as you often have to adopt American standards and clearances in parallel to other internationally adopted schemes or your own local one. But for a long time, the costs justified the prospects of visiting, simply because of the access you get to American markets. With Trump adopting "America first", a lot of people will just not bother deal with travelling to the USA anymore.