The ruins of a lost civilisation are unveiled in the British Museum’s latest blockbuster. It fills the same huge gallery that recently housed colossal Egyptian statues and has previously displayed the wreckage of a Viking ship. The world it uncovers feels just as vanished and remote, yet the archaeological fragments on view are not amphorae, battle axes or Celtic brooches, but pieces of the American Dream.

Here is a US flag, faded to grey. Here is a diagram of an Apollo rocket, icon of the far-off age when President John F Kennedy sent Americans to the moon. Here is the Great American Nude — not to mention great American candy, gas stations and movie stars.

Even the title of The American Dream: Pop to the Present has a savagely tragicomic ring to it now. I don’t know how far back this big exhibition of prints and other graphic works by American artists from the 1960s onwards was named, but it looks pretty damn odd on big banners outside the British Museum while President Trump is driving American democracy into a wall, reversing and driving at the wall again.

This ambitious survey can only add to the disturbing evidence that the wealthiest and most powerful nation is falling steeply into an abyss where its greatest moments become distant memories — if that, for amnesia is part of the illness consuming Trump’s America. I am not joking about the archaeological atmosphere. I was consumed with uneasy nostalgia, and not just because when you leave the exhibition shop you step straight into a hall of ancient sculpture. Looking at the art of Jasper Johns, including a print that gives a coat hanger the sublime authority of a Rembrandt portrait, not to mention at Robert Motherwell’s lithographs of abstract expressionist splash-marks or powerfully chaotic prints by Willem de Kooning, I understood two things very clearly. There is such a thing as American civilisation. And we are watching it die.

The British Museum’s latest show brings together great pop and abstract expressionist images from the US. In the age of Trump, they seem like relics from a lost civilisation

The atmosphere of this show — spacious, light, yet serious — reminds me agonisingly of great American museums where I first saw the art celebrated here. A cardboard door by Robert Rauschenberg, a Hollywood sign by Ed Ruscha — these triumphant American artworks are the kinds of cultural totems you can admire in the elegant settings of New York’s Museum of Modern Art or Washington DC’s National Gallery of Art. How important are those institutions today? They can put on protest exhibitions or go on strike, but who cares? Real cultural power in modern America lies with reality television and conspiracy websites.

Printmaking, extensively on show here, is an innately civilised artform. Ever since it took off in Europe in the 15th century it has been used by artists — Albrecht Dürer was among the first — to create spectacular yet often refined images. In the 20th century the art print was taken to new heights by Picasso and the German expressionists, before being revolutionised in the age of pop art. Yet even when it means a screenprint by Andy Warhol, there is something delicate and archival about the printed image. It needs to be kept safe in collections like that of the British Museum, which owns 70% of the works in this exhibition. This papery, fragile quality adds to the sense of wandering among relics of a lost civilisation.

It seems from these clues to have been an admirable one. It believed in freedom but not in some crass indulgent way; the freedoms taken here are imaginative. Rauschenberg makes an enigmatic disc out of raw paper pulp, Ruscha photographs every building on the Sunset Strip. It was a civilisation of great self-confidence where even liberal artists found beauty in the American flag.

When did it all go wrong? When did the decline of American civilisation start? Was it when JFK was assassinated, or when Richard Nixon brought lies and surveillance into politics? Warhol marks both with haunting images of a grieving Jackie and a monstrous green-faced Tricky Dicky.

Obviously you can’t expect this decent exhibition to tell you how JFK’s America decayed so profoundly that it could succumb to the zombie authoritarianism of Donald Trump. Or how it can ever get back. All it can do is remind us that once upon a time, not so long ago, you could speak of the American Dream without a shred of irony.

By arrangement with the Guardian

Published in Dawn, EOS, April 2nd, 2017