'That's alarming': CNN host stunned when foreign policy expert says Mattis may have to stop Trump from nuking Iran
CNN's John Berman interviews national security expert Richard Clarke (Screen cap).

Richard Clarke, the former National Coordinator for Security, Infrastructure Protection and Counter-terrorism for the United States, stunned CNN host John Berman on Monday when he said it was possible that Defense Secretary James Mattis will have to personally intervene to stop President Donald Trump from launching a nuclear war.

When discussing Trump's reported frustration with North Korea's reluctance to unilaterally disarm its own nuclear weapons arsenal, Clarke said he feared the president would lash out impulsively by lobbing nuclear weapons at Pyongyang.

"The risk here, John, is the president will get frustrated and do something because of his personal involvement in this," Clarke said, referring to the amount of political capital Trump put in his big meeting with North Korean leader Kim Jong-un.

"You keep coming back on this, you're nervous about what the president would do with North Korea when he gets frustrated, just like you're nervous about the language he used with Iran," Berman responded. "Have you seen any evidence that the actions mirror the words?"

"Not yet," he admitted. "And we do have Secretary Mattis between him and our forces, so if the president wakes up in the middle of the night and is mad at Iran and orders some attack, hopefully the system will resist."

"Do you think it will come to that?" asked a surprised Berman. "That is an alarming notion right now, that you think the defense secretary will have to stop the president from launching an attack. Is it a genuine fear or just a scenario?"

"It is a scenario that I think we have to worry about after watching this president's diplomatic malpractice in the last two years," responded Clarke.

Watch the video below.