How any of this might happen is pure speculation. The important point is that it is not, in any sense, impossible.

But while it is not impossible, it is also not inevitable, nor even likely. Still, several factors could nonetheless collide to create a tragedy. These factors mean that the possibility of the kind of miscalculation that could lead to nuclear war is now greater than at any time since the early 1980s.

It’s time to take this threat seriously again, not only as a menace to American national security, but to our collective existence as a civilization.

Tom Nichols is Professor of National Security Affairs at the Naval War College and an adjunct at the Harvard Extension School. His most recent book is No Use: Nuclear Weapons and U.S. National Security (University of Pennsylvania, 2014) The views expressed are his own. You can follow him on Twitter: @RadioFreeTom.

This piece first appeared in 2015 and is being republished due to reader interest.