"In recent months, Congress has expressed concern that some foreign fighters might exploit the Visa Waiver Program (VWP) to enter the United States and commit acts of terrorism. The VWP allows eligible visitors from 38 European nations and a few prosperous Asia-Pacific countries to enter the United States for short business or leisure stays without first obtaining a visa from a U.S. consulate abroad. Recent attacks by domestic terrorists in Europe and reports of European countries' citizens fighting with armed groups in the Middle East have raised concerns that potential terrorists could travel to the United States with little scrutiny under the VWP. Balancing national security interests against efforts to facilitate international travel through the VWP presents challenges to legislators. The United States has a large travel and tourism industry. In 2013, travel and tourism accounted for 2.6% of U.S. gross domestic product and directly employed nearly 5.4 million Americans. Foreign visitors in the United States account for a disproportionate amount of U.S. travel and tourism spending. International travelers spent about $215 billion in 2013 on passenger fares and travel-related goods and services, which makes tourism the United States' single-largest services sector export."
CRS Insight, IN10246
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html