Almost a decade after Middle Eastern terrorists with expired visas attacked the U.S., the government has failed to implement a security measure to adequately track foreigners like them who enter the country legally but never leave. As a result nearly half of the nation’s estimated 12 million illegal immigrants actually entered the U.S. legally but overstayed their visa, according to a new federal report. That’s because the agency responsible for keeping the nation safe—the Department of Homeland Security—can’t keep track of immigrants who remain in the U.S. after their visas expire. This clearly creates a huge national security issue...