Five of the 19 terrorists who attacked the US on September 11, 2001, had broken US immigration laws. Their leader Mohammed Atta had previously overstayed a visa and should not have been allowed back in. As a Justice Department official put it: "The abuse of US immigration laws was instrumental in the deaths of nearly 3,000 people." It was not going to happen again.

The government set about tightening the rules and their enforcement. Six months after the attacks, Atta's application for a student visa to take flying lessons was approved, and a letter saying so arrived at the flight-training school in Florida. The story caused a fresh outcry. The agency responsible was purged, shut down and replaced. The rules were tightened again, and zealously enforced.