Security expert's 'Warnings' on the future of national security

Former national security official and ABC News consultant Richard Clarke talks about terrorism and historic disasters in his new book.
2:27 | 05/30/17

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Transcript for Security expert's 'Warnings' on the future of national security
And finally tonight, a national security expert warns us that warnings don't always work. He says that officials have routinely ignored catastrophic threats despite strong calls to action. And according to him, it's still happening today. Here's "Nightline" co-anchor Dan Harris. Reporter: On this holiday weekend beefed-up security at parks, parades, and sporting events in the wake of the horrific act of terrorism at the Ariana grande concert in Manchester just a week ago. With ISIS claiming responsibility for the attack, it brings into stark relief this question. Could the rise of this terror group have been prevented? In his new book "Warnings," former national security official and ABC news consultant Richard Clarke says yes. Two years before it was an organized group an American foreign service officer named Robert Ford who was very expert in Syria and Iraq looked at the situation there and said if we don't intervene now and create a pro-american counterweight to the Assad government in Syria there will be a new terrorist group pop up to fill that vacuum. Robert Ford was not believed. And lift-off. Reporter: The new book also explores other historic disasters, from the explosion of the space shuttle "Challenger" to the collapse of the levees in New Orleans after hurricane Katrina. Even the Bernie Madoff scandal. In each case there were people issuing warnings. Clark calls these people cassandras. A Cassandra in Greek mythology was a woman cursed by the gods. She could see future disasters, but no one would believe her. Reporter: Clarke should know. He's been called a Cassandra as a white house official in the run-up to 9/11. No one will believe me. No one will pay any attention to me. There's going a terrible disaster if you you don't do something. And they're saying, look, I lose sleep about this. Were you losing sleep and were you feeling incredibly frustrated? Certainly. Reporter: Clarke believes there's a whole series of current threats that are being ignored. Gene editing. Pandemic disease. Sea level rise. Asteroid impact. These are all phrases that we know. We've heard about. Often in science fiction. The problem is they may become fact. All told not a cheery book. No, I think it's a very cheery book because what we're saying is if we're right about using these human cassandras to predict the future we can prevent most of those disasters.

This transcript has been automatically generated and may not be 100% accurate.

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