Istanbul attack shows need to beef up security outside the checkpoints.

Before Independence Day 2002, the first after 9/11, the White House issued this message:  “As Americans gather for July 4th it will be a time of both celebration and vigilance.”

Almost 15 years later, the nation’s mood is much the same as it heads into another patriotic holiday weekend. Americans will rejoice in their freedom but will remain on alert after the latest deadly terrorist attack, this one on the international airport in Istanbul.

Terrorism has become even more difficult to prevent as Islamic State fanatics, some operating as lone wolves, have widened their hunting grounds to nightclubs, restaurants, train stations and subways — any place where…