Kim Jong Un is a “smart cookie,” President Donald Trump said recently of North Korea’s leader. The Conversation

“He’s 27 years old,” Trump mused. “His father dies, [he] took over a regime. So say what you want but that is not easy.”

Kim, who has assassinated his internal rivals using anti-aircraft guns and chemical weapons, seeks to develop a nuclear missile that can reach the United States. These actions may provoke a “major, major conflict” with the U.S., Trump has said: “I hope he’s rational.”

In my research on political leaders, I’ve found that different people have different definitions of rationality. The core question – “What is my best move?” – is often answered by a leader’s idiosyncratic beliefs, rather than by an immediately obvious logic of the situation as seen by external observers.

The history of dealing with inscrutable foreign leaders is instructive: From Hitler to Saddam to Khrushchev, understanding the other is the most urgent challenge of national security decision-making for the U.S.

To influence Kim’s behavior, we must ask: What is his particular vantage point?