Americans have long felt that NATO isn't doing its job and that the Europeans aren't contributing enough. Trump has accelerated the decline in Atlantic solidarity by offering open contempt for NATO allies as well. The future of NATO now very much depends on Europeans. Can you begin to identify security threats, prepare yourselves and arm yourselves without the US?

The Soviet Union was, by the 1970s and 1980s, relatively stable and predictable. Putin's Russia is much more volatile. Nuclear policy is really in the hands of one person, or a small group of people, instead of a huge party-state apparatus. The possibility of a mistake is greater now.

Putin imagined it would be different. So, like many Russian leaders before him, he imagined that Ukraine was basically Russia, but they speak with a funny accent. Actually, it's not Russia; it has a different identity. It has a very different language. Russians don't automatically understand Ukrainian. And, in particular, the way Ukraine has developed over the last two decades is different from the way Russia has developed.

What is the appeal of Trump, really? It's nostalgic: "Make America great again." Like European nationalists, he has a vision of a "real" America, one which predates globalization, immigration, feminism, the civil rights movement and technological change, an imaginary 1950s to which we can now return. That is actually not very different from the kind of language that Marine Le Pen uses, or parts of the Brexit movement.

Think of the French presidential candidate Emmanuel Macron, Ciudadanos in Spain, Nowoczesna in Poland. These are early efforts to reimagine a liberalism which is neither right-wing nor left-wing in the traditional sense.

The surge in right-wing populism and the phenomenon of Trump are related. You can think of them together as the same problem.

The old battle between Christian Democrats and Social Democrats is now meaningless, not least because the social structures that underlay those parties, the church and the unions, have faded away. Nationalists and populists understood this change earlier; now the rest of the political world needs to understand that the political lines have been redrawn and it's time to change.