Are we sliding back to the chaos of the 1930s?
US President Donald Trump swept through Europe like a hurricane. He asked why his country was obliged to defend its allies, carped about "unfair" trade practices, blasted the UK and Germany as weak on migration and suggested President Vladimir Putin was as credible as America's own intelligence agencies when it came to Russian hacking.
Trump reprised his role as a cheerleader for Brexit and complained that everyone was taking advantage of the US. Negotiating with Putin would be easier than dealing with allies, he said. It was all transactional, about price tags and deals. Values found little airtime.
At almost every step, in tweet after tweet, he sneered at the liberal western order built from the ashes of World War II, underwritten through institutions like NATO and the UN and protected under the US nuclear umbrella, an order that has given much of the world unrivaled peace and prosperity.
Former US Vice President Joe Biden said last week that Trump was (wittingly or otherwise) helping with Putin's agenda, which is above all to break the liberal western order that faced down the Soviet Union and stands for everything the Russian leader despises.
But is that order really in danger, and if so what might replace it? Some hark back to the 1930s, when the aftermath of economic crisis, protectionism, hostility to minorities, the collapse of international institutions and a sense that democracy had failed, allowed fascism to take root.
This parallel can be overdone of course: we live in an age of relatively full employment. We appear not to be on the brink of war, with fascist powers re-arming. Paramilitary groups don't stalk the streets, most nation-states are stronger than they were in the 1930s, and the concept of human rights is now entrenched in democratic societies.
But when in doubt, quote Mark Twain, who is reputed to have said that "History doesn't repeat itself but it often rhymes."
And if some echoes of the 1930s are faint today, there are many contemporary trends that are equally alarming.