The travel and tourism industry, which accounts for about 3% of the U.S. GDP, has long been one of the economy’s most robust sectors, particularly when it comes to trade: The U.S. had posted a trade surplus in travel every year this century. Until this year. Advertisement A drop in foreign visitors to the U.S. caused the real value of exports of travel services to fall at a 7.8% annual rate in the first quarter, according to the GDP report released Wednesday. The U.S. Travel Association says