TRUMP Tower, in midtown Manhattan, has become a modern-day Mount Vernon. Tourists have long visited George Washington’s homestead. Now they venture through Trump Tower’s brass doors to ogle the decor—“it’s so gold,” said a German teenager standing near the lobby’s waterfall on a recent afternoon—or buy souvenirs. The Choi family, visiting from South Korea, wandered the marble expanse with their new “Make America Great” hats (three for $50).

The question for America’s hoteliers and airlines is whether such visitors are just anomalies. A strong dollar is one reason for foreigners to avoid visiting America. Donald Trump may prove another, suggests a growing collection of data. Yet measuring the precise impact of Mr Trump’s presidency on travel is difficult. In addition to the currency effect, many trips currently being taken to America were booked before his election. Marriott, a big hotel company, reported an overall increase, compared with a year earlier, in foreign bookings in America in February.

But Arne Sorenson, Marriott’s boss, has voiced concern about a potential slump in tourism. In February, ForwardKeys, a travel-data...Continue reading