The White House announced changes Monday to the government's visa-waiver program to try to stop those who have visited conflict zones from easily boarding American-bound commercial flights, a move intended to prevent an attack in the United States similar to the ones that struck Paris.
But the new measures - which include potentially higher fines for airlines that fail to verify their passengers' identities and increased information-sharing between countries - are limited, and White House officials acknowledged that they would need Congress to pass legislation to further tighten controls.
The visa-waiver program - a special travel arrangement to ease the flow of European tourists and other visitors from friendly countries - poses a far greater threat to national security than the Obama administration's highly criticized plan to allow 10,000 Syrian refugees to enter the country, according to law enforcement experts and officials.
