In 2014 I published a book called “America in Retreat,” with the subtitle, “The New Isolationism and the Coming Global Disorder.” Though an entire chapter is devoted to a critique of Tea Party foreign policy, it was mainly a lament about what I saw as President Obama’s imprudent retreat from America’s global responsibilities and the risk of returning to the disastrous foreign policy mind-set of the 1930s.

Silly me. I wrote the book one administration too soon.

That’s the conclusion to draw from Donald Trump’s long-promised and now bluntly delivered imposition of steel and aluminum tariffs on Mexico, Canada and the European Union. And that was just after Treasury Secretary Steven Mnuchin decided to put tariffs on China “on hold” to allow negotiations to continue.

What was it that Sarah Palin once said about Obama’s foreign policy — that he was “coddling enemies and alienating allies”? Well, move over, Barack.

Those tariffs on China might still be on — with this administration, inconstancy and idiocy seem to contend like wrestlers in a W.W.E. match — but that would only compound the damage. Protectionism anywhere is invariably bad for local consumers and the global economy, but American protectionism is infinitely worse. It’s a betrayal of the liberal-international order we founded nearly eight decades ago; an invitation to anti-Americanism; a rebuff to our friends; and sometimes (Boston Tea Party, anyone?) a prelude to war.