Others cited violence and safety. Marika Treichel, who lives in Denmark, wrote, “I have always dreamed of visiting the US. But the rise of gun violence and political chaos has made me want to cancel all future travels to the U.S. until I can feel safe as a tourist.”

This has been a strong year for the U.S. dollar, which makes travel more expensive for other currencies — though exceptions make that an unsatisfying explanation for the tourism drop. The Canadian dollar, for example, is weaker than it has been in previous years (despite a summer surge), yet Canadian tourism to the United States was up 14.8 percent January through April.

Within Europe, the tourism declines were largest in Switzerland at nearly 28 percent, Belgium at 20 percent and Britain at 15.5 percent. Britain accounts for the largest share by country of European arrivals in the United States, with 4.5 million tourists last year, making its slowdown significant. (Asian tourism was about the same as last year — up .6 percent — mainly due to a surge of South Korean travelers, up over 15 percent in the first quarter.)

“The international travel market is ultracompetitive, and the U.S. is falling behind,” said Roger Dow, the president and chief executive of the U.S. Travel Association, a nonprofit that promotes travel to and within the United States, in a statement.

A report released in April by the World Economic Forum showed the United States falling two spots in its rankings of the top 10 most popular countries for tourism in the world. The United States fell to number six, passed by both Japan and Britain.

The economic picture is less straightforward, however. The Commerce Department’s National Travel and Tourism Office reported a 2.5 percent increase in spending by international visitors to $83.4 billion in the first four months of the year compared to the same period in 2016.

Some of the decline in first quarter results may be because of the shift of the Easter and Passover holidays, when travel usually spikes. Those occurred in March of 2016 and April this year, possibly skewing first quarter figures. April figures ease the overall decline of foreign visitors to the United States from 4.2 percent to 1.2 percent. A boost in arrivals from Canada, up 7.8 percent through April after two years of declines, helped offset slowdowns from Mexico at 4.9 percent for the first four months of the year and Britain. at 6.9 percent for the same period.