With his famed utterance that everyone is entitled to their own opinions, but not their own facts, the late Daniel Patrick Moynihan had to have known, on some level, that he was offering a cliche destined to last the ages.

But the truth, like history, and so many other things these days, just ain’t what it used to be.

We live in age where “alternative facts” are so much in ascendance that it is possible, as the Economist observed, for the president of the United States to both ad...