President Donald Trump tweeted on Friday morning the United States is “locked and loaded” for a military confrontation with North Korea. This comes after North Korea threatened to send nuclear missiles to Guam, a U.S. territory, and President Trump’s shot back with threats of “fire and fury like the world has never seen.”

North Korea has been in a constant state of frozen war with South Korea since the 1950s. South Korea has traditionally leaned toward attempts at negotiating peace with the North, but in recent years, South Korea has been considering a break from U.S. policy and pursuing a nuclear weapons program of their own.

We speak with Robert Einhorn, a senior fellow at the Brookings Institution, who says that South Koreans are increasingly afraid that the U.S. would throw them under the bus in case of a North Korean first strike. In an article for The Bulletin of the Atomic Scientists, Einhorn says that Trump “has reinforced worries in Seoul that the public mood in the United States is becoming more isolationist.”