Mr Donald Trump's travails with his "Muslim ban" make it easy to dismiss the whole idea as an aberration that will swiftly be consigned to history by the judicial system and the court of public opinion. But that would be a misreading. The ban on migrants and refugees from seven mainly Muslim countries was put together clumsily and executed cruelly. But it responded to a hostility to Islam and a craving for security and cultural homogeneity that is finding adherents across the Western world - and not just on the far right.
Even if Mr Trump's ban is withdrawn or amended, it will probably be just the beginning of repeated efforts - in the US and Europe - to restrict migration from the Muslim world into the West.
There certainly should be no doubt about the radicalism of the thinking of some of Mr Trump's key advisers. Mr Michael Flynn, the President's embattled national security adviser (who resigned yesterday), and Mr Stephen Bannon, his chief strategist, believe that they are involved in a struggle to save Western civilisation. In his recent book, The Field Of Fight, Mr Flynn insists: "We're in a world war against a messianic mass movement of evil people, most of them inspired by a totalitarian ideology: radical Islam." Mr Bannon holds similar views. In a now-famous contribution to a seminar at the Vatican in 2014, he argued that the West is at the "beginning stages of a global war against Islamic fascism".
The fact that Mr Trump's closest advisers believe they are engaged in a battle to save Western civilisation is key to understanding the Trump administration. It helps explain why the President, in his inaugural address, pledged to defend the "civilised world" - not the "free world", the phrase that would have been naturally used by a Ronald Reagan or a John F. Kennedy.
This tendency to conceive of the West in civilisational or even racial terms - rather than through ideology or institutions - also helps explain the Trump team's sympathy with Mr Vladimir Putin's Russia and hostility to Dr Angela Merkel's Germany. Once the West is thought of as synonymous with "Judeo-Christian civilisation", then Mr Putin looks more like a friend than a foe. The Russian President's closeness to the Orthodox church, his cultural conservatism and his demonstrated willingness to fight brutal wars against Islamists in Chechnya and Syria cast him as an ally.
By contrast, Dr Merkel's willingness to admit more than a million mostly Muslim refugees into Germany makes America's alternative right regard her as a traitor to Western civilisation. President Trump has called the German Chancellor's refugee policy a "catastrophic" error.
Through his Breitbart news service, Mr Bannon forged close ties with the European far right, who share his hostility to Islam and immigration. The belief that the West is engaged in a mortal struggle with radical Islam clearly animates France's National Front leader Marine Le Pen, who recently argued: "Washington, Paris and Moscow must form a strategic alliance against Islamic fundamentalism... Let us stop the quarrels and unnecessary polemics, the scale of the threat forces us to move fast, and together."
These views are not confined to the political extremes in France. Mr Francois Fillon, the centre-right's candidate in the presidential election, recently published a book called Conquer Islamic Totalitarianism, which contains the Flynn-like declaration that "we are in a war with an adversary that knows neither weakness nor truce".
France's former Europe minister, Mr Pierre Lellouche, has also just brought out a book called War Without End, which argues that Islamism is the 21st-century equivalent of Nazism.
Far-right parties with a Trumpian view of Islam are also prospering in the Netherlands and in Germany. The Freedom Party, led by Mr Geert Wilders, is set to top the polls in next month's Dutch elections - although it is unlikely to enter government. In Germany, the Alternative for Germany party has surged in response to the refugee crisis, and is likely to become the first far-right party to enter the country's Parliament since 1945. Some in the British government believe that hostility to immigration from the Islamic world - more than Europe - was behind the discontent that triggered the Brexit vote last year.
Sympathy for the Bannon-Flynn-Trump view of Islam extends beyond the US and Europe. A belief that their nations face an elemental threat from radical Islam is also an animating force on the right wing of Indian and Israeli politics.
Even if Mr Trump loses the battle over his executive order on refugees and immigration, he is likely to return to the fray with further measures. That is because his closest advisers and many of his strongest supporters will remain driven by a deep suspicion of Islam and a determination to stop Muslim immigration.
There will also, almost inevitably, be further extremist attacks in both the US and Europe that will feed this fear and hostility. Meanwhile, the long-term demographic trends that create pressure for migration from Muslim countries to the US and Europe will only increase in the coming years. The population of impoverished, largely Muslim, north Africa is much younger than that of Europe, and growing fast.
The polemic over Mr Trump's "Muslim ban" will not be an isolated event. On the contrary, it is a foretaste of the future of politics in the West.
THE FINANCIAL TIMES