Theresa May is reviled for her weakness. But, as so often, cliches deceive. No British prime minister has found the strength to condemn an American president as she condemned Donald Trump since the Anglo-American alliance began in the Second World War. Anthony Eden maintained a public silence as Eisenhower destroyed his premiership, and Britain’s imperial pretensions, when he stopped the Suez adventure of 1956.

Harold Wilson ignored Lyndon Johnson’s pleas to send British troops to Vietnam. But he infuriated the radicals of the 1968 generation by diplomatically refusing to speak out against the war. Thatcher and Reagan, Major and Clinton had their private arguments about Grenada and the IRA. Nothing they said matches the forcefulness of May’s out, loud and proud denunciation of Trump for sharing the “hateful narratives” of British fascists.

It has been comic to watch the shock with which politicians greeted Trump’s endorsement of Britain First. They must have known he has spent his life in the grey zone between the right and the far right. If they didn’t, we have a Foreign Office paid to set them straight. Only last week, Trump reminded us where his fanatic’s mind lingers when he revived the bitter, broken fantasy that America’s first black president was an illegitimate African interloper. There is no racist lie he will ever reject or disown.

Britain’s leaders will not see it. May’s criticism was unprecedented but it remained a wholly inadequate response to an unprecedented US president. Britain and America are still allies, the PM said, as she tried to repair a shattered relationship. Trump may be a “buffoon” but he is still Britain’s “best friend”, the rightwing press told its readers. Theirs was the authentic voice of the politically left behind, who will never accept the world has changed until it blows up in their faces.

Allies stand by their friends when they are in trouble. Trump turned on Sadiq Khan, London’s Muslim mayor, when the capital was being attacked by Islamists, for reasons that are too transparent to waste time on. Intelligence sharing between GCHQ and the US National Security Agency is the one clear benefit of the otherwise hazy “special relationship”. When he needed a fresh lie to feed to his credulous supporters, Trump was happy to trash it by conjuring the fantasy from the pit of his dark imagination that GCHQ had helped the Obama administration tap his phone.

Imagine that a US president had retweeted and then defended the Islamist equivalent of Britain First and refused to apologise or retract. I think the reaction of the Tory party and press would not have been so mild. Yet the distinction between neo-fascism and Islamo-fascism is a distinction without a difference. Both share the fundamental conviction that Muslims and non-Muslims cannot live together. Both are violent. (Indeed, in the US, rightwing extremists plotted or carried out nearly twice as many terrorist attacks as Islamist extremists.) And the threat from both has moved online.

The “it couldn’t happen here” school of commentary, so powerful in what passes for the “national conversation”, was quick to say that, while Britain First has 1.7m Facebook likes, it barely musters a handful of militants to invade halal butchers. If you wanted to match their complacency, you could add IS is merely a web-based movement now Raqqa has fallen. That is hardly a soothing thought, however, when radicalisation is increasingly an online phenomenon. Thomas Mair was not a member of Britain First. He still shouted “Britain first” when he murdered Jo Cox because he was indoctrinated on far-right websites to hate race traitors as thoroughly as IS indoctrinates recruits who have never left the UK to hate the kuffar.

The leader of the free world has not only legitimised Britain First as he has legitimised so many other violently unhinged movements and ideologies. He has driven traffic and attention to its sites. One day, a “lone wolf” who has stared too long and hard at the light from his flickering screen may make us pay.

‘Ally” is a strange word to describe a country whose leader delights in threatening your security. Stranger still when Trump has looked for himself in others when seeking foreign friends and preferred kleptomaniac autocrats over democratic leaders. On climate change, the Iranian nuclear deal and the Muslim travel ban, Britain is not “allied” with Trump’s America but on the other side. We have expressed exactly the same objections as the other leading EU countries, but there’s the rub. For a generation, the European Union has been the British right’s “other”. It has defined itself against the EU and based its utopian dream of a revived greatness on freeing Britain from Brussels.

It is not only a nostalgia for 20th-century alliances that stops conservatives from understanding how far away Britain is from Trump’s concerns, but their forlorn hope that the US will save it from the folly of cutting itself off from our true friends in the world’s largest free trade area. The notion that Trump will compensate Britain by offering a generous trade deal with the US does not survive contact with reality. Before he advertised his admiration for Britain First, Trump announced himself a believer in “America First”, a slogan coined by US appeasers of Nazi Germany, as he must know. He does not grant trade deals, he destroys them. He has pulled the US out of the Trans-Pacific Partnership and may walk away from the North American Free Trade Agreement.

Were they not lost in magical thinking, Conservatives, diplomats and generals would be hugging our European allies close. Even if they were determined to go ahead with Brexit whatever the cost, they would recognise that the US could not be depended upon and be proposing new systems of European defence co-operation. They would not engage in the wishful thinking that Trump will be out by 2020. They would not keep muttering that falsest of consolations of the past decade that we will “return to normal” and all will be well. They would have the intellectual strength to accept the possibility that “normal” may never return.

“To name things wrongly is to add to the misfortune of the world,” said Albert Camus. When Britain names America as its ally, it only heaps more misery on its already considerable misfortune.