According to the US State Department, a VWP traveler without a visa, “must have authorization through the Electronic System for Travel Authorization (ESTA) prior to boarding a U.S. bound air or sea carrier.
ESTA is a web-based system operated by U.S. Customs and Border Protection (CBP) to determine eligibility to travel under the VWP to the United States for tourism or business. Visit the ESTA webpage on the CBP website for more information.”
“The VWP utilizes a risk-based, multi-layered approach to detect and prevent terrorists, serious criminals, and other mala fide actors from traveling to the United States.” Travelers to the US using the VWP should expect to be vetted prior to their US departure, on arrival, and during any future air trail within the US.
The US Department of Homeland Security “coordinates with the National Counterterrorism Center (NCTC) to vet ESTA applications to ensure that travel authorizations are not issued to individuals who pose a threat to national security.
In November 2014, DHS began requiring ESTA applicants to provide additional information to further enhance its ability to identify applicants on the U.S. terrorist watchlist.” “DHS automatically screens all ESTA information against numerous U.S. law enforcement and counterterrorism databases, as well as INTERPOL databases, while upholding strict privacy standards. “