“The person who made the statements doesn’t know much about foreign policy or nuclear policy or the Korean Peninsula or the world generally,” Obama said at a news conference at the close of the Nuclear Security Summit.

Obama described the U.S. nuclear umbrella for Japan and South Korea, in place of their own arsenals, as “one of the cornerstones of our presence in the Asia Pacific,” which has provided the U.S. peace, prosperity and flowing commerce.

“It has prevented the possibilities of a nuclear escalation and conflict,” he added. “You don’t mess with that. It’s an investment that rests on the sacrifices that our men and women made” in World War II.