Frum remarks, in his Acknowledgments: "No single person could possibly plumb the foulnesses of the Trump presidency." In this book he gives a more than adequate summary of Trump's foulnesses. One's appetite sickens as one is reminded of them. While Gibbon left "all licentious passages...in the obscurity of a learned language", Frum gives them in plain English.

But how gloomy should all this make us? Conservatives are naturally tempted to be cultural pessimists. The world is not what it was, is quite clearly going to the dogs.

And yet the American Republic has repeatedly demonstrated its capacity to regenerate itself. Things have often been pretty bad in the past - a point Frum seldom acknowledges. Every president arrives in Washington promising to bring about "a new birth of freedom".

Barack Obama has wonderful manners, an ability to behave with grace and restraint on any occasion. Trump, with his ability to behave like an oaf on any occasion, is a corrective to that.

But I am allowing myself to get blinded by personal antipathy. Frum himself claims, after describing how so many Republicans first attacked and then for the sake of their own advancement made their peace with Trump, that the President has "ripped the conscience out of half of the political spectrum and left a moral void where American conservatism used to be".

That is overdrawn. Trump will inspire a reaction too. Reputable Republicans and Democrats will work out how to frame an appeal to the whole nation, and not just to the prosperous half of it. This will entail a recognition that some of the issues on which Trump campaigned, from immigration to decrepit infrastructure to the condition of the working class, were well chosen, and need careful attention.

In my opinion (which like many of my opinions could turn out to be sadly mistaken), the great American Republic will emerge stronger from this presidency, its institutions strengthened by the exertions required to restrain and correct Trump's excesses, its constitution vindicated, its political parties brought closer to the people they claim to represent.