Former CIA Director David Petraeus spoke on Sunday at a conference on national security and cyber issues taking place at the Tel Aviv University.

In his remarks, Petraeus said he welcomes the United States’ recent withdrawal from the Iran nuclear agreement because, he said, “it will see much greater pressure on Iran, not just in areas covered by the nuclear deal, but also with regard to its missile program and Iran’s malign activities… in the rest of the Middle East.”

Petraeus was asked what three pieces of advice he would give President Trump if he had a few minutes with him.

“I think I’d just limit it to one, and I would focus on the threats to America’s critical infrastructure. My concern is the concept of idea of a cyber weapon of mass destruction but in the hands of an entity that’s very hard to deter,” he said.

Nation states can be deterred, Petraeus continued, but “I don’t know how you deter an extremist element like ISIS which is willing to blow itself up on the battlefield to take us with it. How do you keep an organization from hitting the send key if they have the ability to shut down the electrical grid of the eastern United States and to keep it down?”