I am not going to take a position here on whether Mr. Trump is a genius, a madman, or something in between.  I do want to criticize the notion that he “acts on whims” and is “volatile.”

How he gives such an impression is easy to see:  In negotiating with both friends and enemies, he blows both hot and cold, depending on time of day.  What those who think he is acting on whims overlook is that he believes in blowing both hot and cold.

Consider the game “Rock, Paper, Scissors.”  If the other player knows you will always play Rock, then he will always play Paper, and he will always win.  But if you play Rock one-third of the time, Paper one-third of the time, and Scissors one-third of the time, so that he can't predict what you will do, then he won’t be able to gain an advantage.

In the mathematical theory of games, playing Rock all the time is called a “pure” strategy, and playing each of the three moves one-third of the time is called a “mixed” strategy.  It can be shown that in the sort of winner-take-all game in which there is no advantage to cooperation, there is always some best strategy, though it may not be one which will always win.   Often the best strategy is a mixed strategy.

This is intuitive.  Keep ‘em guessing.  In fact, keep ‘em guessing not only about what you are going to do, but even about some aspects of what you know and believe, and who you listen to, and what it would take for you to change course.

Needless to say, not all purely competitive games are like Rock, Paper, Scissors.  In that game, the best strategy is to play each move with equal probability, but in another kind, the best strategy may be different – say, to play Move A one-quarter of the time, Move B one-quarter of the time, and Move C one-half of the time.  It depends on how the game is set up -- and also on the situation on the board. 

On most issues, Mr. Trump’s long-term preferences are known.  For example, he has been talking about tariffs for decades.  When he blows hot and cold, I think he is playing a mixed strategy.

Mixed strategies are hard to play in a political system which requires consensus.  The reason is that in order to keep the other side guessing, one has to play one’s cards close to one’s chest.  Since one’s allies might leak, one may have to keep them just as much in the dark as one’s adversaries are.  Being in the dark, they might panic.  They might withdraw their support.  Markets may roil.  For all these reasons, the game one is really playing (whether he knows it or not) may be much more complicated than the game one may seem to be playing, and it may even change as it’s going along.

You might argue that Mr. Trump is playing the right game or the wrong one, or with the right mixed strategy or the wrong one, or that he is playing it well or playing it badly.  But I don’t think it persuasive to suggest that he is volatile or acting on whims.