Someday this White House will face a sudden, immediate and severe foreign-policy crisis. It’s almost a miracle it hasn’t happened already. George W. Bush had 9/11 less than eight months into his tenure; John F. Kennedy had the Bay of Pigs three months into his presidency and the Cuban missile crisis the following year. In two years Donald Trump has faced some turbulence, but not a full-fledged crisis.

Such good fortune won’t continue forever. I sometimes ask past and present officials of this administration their thoughts on a crisis, and how the White House would handle one. They are concerned.

What might such a crisis look like? History resides in both the unexpected and the long-predicted. Russia moves against a U.S. ally, testing Washington’s commitment to Article 5 of the North Atlantic Treaty; a coordinated cyber action by our adversaries takes down the American grid; China, experiencing political unrest within a background of a slowing economy, decides this is a good time to move on Taiwan; someone bombs Iran’s missile sites; Venezuela explodes in violence during a military crackdown; there’s an accidental launch somewhere.

Maybe it will be a wild and deliberate act that brings trouble, maybe not. The historian Margaret MacMillan said a few years ago in a radio interview: “I think we should never underestimate the sheer role of accident.”

What does it take to handle a grave crisis successfully, beyond luck?