Fundamentally, Mr. Trump has no philosophy, does not think in terms of “policy” (as we normally understand that term) and sees essentially everything through the prism of what benefits Donald Trump. Thus, his decisions as President constitute “an archipelago of dots,” as I wrote in my recent book, not a coherent pattern resting on principles and logic. Mr. Trump is not a conservative. He is not a liberal, either. He is simply entirely pro-Trump.

His favourite lawyer, Roy Cohn, once described how former senator Joseph McCarthy (a Republican from Wisconsin) became an anti-Communist: “Joe McCarthy bought anti-communism in much the same way as other people purchase a new automobile. The salesman showed him the model; he looked at it with interest, examined it more closely, kicked the tires, sat at the wheel, squiggled in the seat, asked some questions and bought. It was just as cold as that.”

It is entirely possible that Mr. Cohn taught Mr. Trump this very lesson about “conservatism.” Whatever the background, the contrast between Mr. Reagan and Mr. Trump could not be more vivid.