THE Italian dictator Benito Mussolini ruled Italy for 17 years after a comic opera coup in which a band of his followers marched on Rome in 1922. He rapidly extinguished democracy, installed himself as "Il Duce" and ran a delinquent autocracy, with some narrow success, until he was finally strung up by communist partisans in 1945. It is a measure of the panic that has afflicted liberal America that the 45th president of the United States is being compared to the Italian fascist leader – not just by the demonstrators outside Trump Tower, but in political journals like The Atlantic and Salon.

Take away the bouffant hair and there is a facial resemblance. Like Mussolini, Trump is a vain nationalist demagogue, with a strong strand of racism and an ugly turn of speech. But there the comparison becomes strained. After all, Mussolini was a ex-socialist intellectual and journalist who read Plato and Nietzsche in his spare time. The Donald probably thinks Nietzsche is a sexually transmitted disease. Italian fascism was a repellent if compelling ideology which revered the state as the embodiment of an almost mystical “will” and advocated military confrontation for its own sake. Donald Trump's religion is summed up in his best-selling book, The Art Of The Deal and has all the ideological sophistication of Only Fools And Horses.

Trump is first of all a self-interested opportunist, rather like America's last worst president, Warren G Harding, who occupied the White House after the First World War and turned it into an engine of self-enrichment. There is no place for high-minded idealism, of right or left, in Donald Trump’s White House. He doesn't see America as a “shining city on a hill”, like Ronald Reagan, but a shopping mall ripe for redevelopment. However, The President-elect is a brilliant opportunist and self-publicist who has an intuitive understanding of the weakness of both the left and the liberal capitalist establishment in the West: their aversion to nationalism.

Donald Trump has weaponised nationalism; turned it into an almost unstoppable political force. His long march to Washington looked as ludicrous and vainglorious as Mussolini’s march on Rome, but his appeal to crude national interest emasculated the established political parties with a ruthless effectiveness that Il Duce would have approved. His slogan, Make America Great Again, may sound like the kind of vapid cliché to which all US presidents subscribe along with reverence to the flag and creepy references to “scripture”. But no-one has actually tried to put America First, as a principle of political action, since the days of Herbert Hoover in the 1930s.

America First means isolationism, protectionism and ethnic exclusion. It is a repudiation of America's geopolitical strategy since the Second World War, which has been founded on free trade, globalisation, and bolstered by the exercise of both hard (military) and soft (cultural) power across the planet. Since the Second World War, America has been flattered to regard itself as a beacon of freedom and prosperity to the world. Its motto was Kennedy's inaugural promise (as the Berlin Wall was being planned), to “pay any price, bear any burden, meet any hardship, support any friend to ensure the success of liberty”. Donald Trump's answer to JFK is to build his own 1000-mile wall which, if it is ever erected, will serve as a monument to the collapse of American idealism.

Trump plans to scrap the North American Free Trade Agreement, impose punitive tariffs against Chinese and other imports and tear up international engines of strategic co-operation like Nato and the United Nations. In the 1930s, this economic nationalism was called autarky – and it greatly prolonged the Great Depression. It was accompanied by a romantic and often belligerent nationalism that found its purest expression in Mussolini's fascism, but affected most Western nations. Trump may not be interested in military expansion, but he has reawakened this autarkic demon. It is reflected in his admiration for the Russian President, and Vladimir Putin's self-interested militant nationalism.

Trump is part of a nationalist wave which is, paradoxically, international and currently sweeping Europe. Donald Trump's victory was celebrated first of all by the right-wing Hungarian leader, Viktor Orban, who pronounced the end of “liberal non-democracy” and a return to nationalist, Christian “common sense”. Next in line was Marine le Pen, the leader of the far-right French National Front and a contender in next year’s presidential elections. She has similarly refashioned her party to appeal to the dispossessed in industrial backwaters of France, where globalisation is synonymous with low pay, unemployment and insecurity, and where fear of Muslim immigrants has been inflamed by events like the Paris shootings.

The bouffant Geert Wilders, leader of the anti-Muslim Dutch Freedom Party, hailed Trump's victory as a “patriotic revolution”, and hopes it will bring him success in their forthcoming elections. Austria already has a far-right president, Norbert Hofer. Right-wing anti-immigrant parties are on the march even in the supposedly liberal Nordic countries like Finland, Norway and Denmark, where they have been entering governing coalitions. The Danish immigration laws are now the harshest in Europe and include seizing money and valuables from immigrants when they cross the border.

But the epicentre of this alt-right nationalism is of course Britain, home of the Brexit revolution. The image of Nigel Farage acting as a chaperone to Theresa May in her first meeting with Donald Trump may be a image best forgotten. But the former Ukip leader believes he will play a leading role in the new post-Brexit special relationship, perhaps as US ambassador. And he might. Donald Trump has described his victory as “Brexit plus, plus, plus”. He received counselling from Nigel Farage and his advisers throughout the presidential campaign.

Theresa May's congratulation of Donald Trump’s victory was singularly obsequious. As we saw at the Conservative Party conference, the UK Tories are now largely indistinguishable from Ukip, preoccupied with immigration and even proposing that firms compile registers of migrant workers. It is strangely fitting that the Trump revolution should have begun in Britain, the junior partner in America's post-war project. For Brexit has destroyed the foundation of British and American foreign policy in that period, which was built on UK membership of the European Union. They hang together.

Brexiteers are excited by the promise of a new special relationship with America based on self-interested nationalism. It's not entirely clear why they expect Trump to offer special deals to the UK which he doesn't extend to other countries. But there is no doubt that Trump will continue to see Britain, or rather England and Wales, as his ideological second home. Scotland, of course is different, and has bred a civic nationalism which is internationalist, social democratic and welcomes immigrants.

The First Minister, Nicola Sturgeon, even tried to have Trump banned from Britain because of his views on race. The collision between these two nationalisms may not be long delayed. The Donald has considerable investments in Scotland, not least in his golf courses in Aberdeenshire and Ayrshire. His mother came from the Isle of Lewis. He will surely drop by.

Some UK unionist commentators insist that the difference between Trump and Sturgeon is only skin-deep. These are the people who used to claim that the SNP is fascist because “Mussolini was a nationalist too”. The left has been unable to come to terms with the durability and diversity of nationalism, largely because it sees the engine of history as the international proletariat. Like neo-liberals, socialists see nations as essentially irrational, pre-modern anachronisms. But there is no such thing as an international working class, only working people living in pre-existing moral communities called nations. And the inconvenient truth is that nationalism and democracy have gone hand in hand since the days of American and French Revolutions. The democratic revolutions of 1848, which inspired the Communist Manifesto, were at the time called the Springtime of Nations as European nations asserted themselves against the old feudal dynasties. But as the celebrated Scottish writer, Tom Nairn, always argued, nationalism is Janus-faced. It has an open, democratic anti-imperial face and a dark side of ethnic and racial supremacism. Keeping it on the democratic straight and narrow requires eternal vigilance.

Which brings us back to Donald Trump. His dark nationalism has undermined the liberal democratic establishment, but he has also invaded the territory of the left. Trump's politics echo much of the anti-capitalist rhetoric of Millennials who are right now demonstrating outside his hotels. He is similarly opposed to globalisation and corporate-sponsored trade deals like TTIP. Trump has promised to launch a huge Keynesian investment and job creation programme partly financed by repatriation of the profits of American corporations like Apple. (Whisper it, but Trumponomics actually does echo Mussolini, who read and approved of “every word” of John Maynard Keynes economic doctrines.)

If Donald Trump truly represents the “end of the West”, the eclipse of liberal democracy and globalism, then the challenge for the left is to find a way of developing a progressive form of democratic civic nationalism to counter delinquent, racial, nativist forms that will be roaring back in the wake of Trump. The President-elect and Nicola Sturgeon embody the foul and fair aspects of the nationalist Janus. And it is no exaggeration to say that the future of European civilisation may depend on which one prevails.