“He’s won,” I shouted at the television. “Bloody hell, he’s won.” As Donald Trump read out his surrender-to-terrorism message this week, I realised who was now his master: Osama bin Laden. Trump spoke with his eyes down, like a hostage under duress. His was an America frightened, incoherent, illiberal, fearful of some unknown power. He was the voice of a cowering nation.

Bin Laden, or at least his ghost, has moved a step closer to his goal on 9/11: to put America in thrall to an Islamic ascendancy. He wanted an America that, as Trump put it, “does not know what the hell is going on”, that is “out of control”. He wanted an America that “does not care” about its customary freedoms. He wanted all Muslims to be America’s enemies. Trump duly delivered. He was Bin Laden’s acolyte, his accomplice, his stooge.

Britons should beware of criticising Trump. They are not innocent of his crime. Godwin’s law states that the longer a political argument runs, the sooner it reverts to the second world war. Someone “plays the Hitler card” – and eventually loses. David Cameron played the card in last week’s parliamentary debate on Isis. So did Labour’s Hilary Benn. They equated Isis to the Nazis, and their opponents to appeasers of 20th century fascism. They summoned up the bombers against Muslim cities and demanded curbs on civil liberties commensurate with the declared threat. It was Trumpism for slow learners.

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To compare any threat facing Britain or America at present to Hitler’s Germany is ludicrous. It is historically illiterate. It is an offence to all who suffered and died in Hitler’s war. It is an offence to Britain’s allies round the world. It is an offence to language. As the House of Commons cheered on the bombers (and swore to send no ground troops), I wondered how it might react if Britain really did face another Hitler. Would it join Donald Trump, quaking with terror under the nearest table?

Fear is the most potent of political weapons. It is more deadly than greed, ambition or love of home. It is dangerous because it feeds on the irrational in human nature. Like a nuclear weapon it should be kept locked away, for use only in extremis.

Yet in recent months fear has been deployed by ministers and opposition politicians, generals, spies, police officers, newspaper editors and television producers. Every two-bit nutcase is declared “an existential menace”, a threat to “national security”, a saboteur of our “civilised values and way of life”. I could not believe BBC radio listeners being invited to boast about cancelling their holidays out of fear.

No one really believes that Britain’s values and way of life are so feeble as to fall to a machine gun or a grenade. No one really thinks that Muslim travellers could undermine the American way of life. Guns kill and bombs destroy buildings. But that does not threaten “our very existence”. The likelihood of an English caliphate is precisely zero, however much it suits politicians and the security lobby to claim otherwise.

So why do Cameron and Benn repeat Godwin’s law? Why do Trump’s supporters have so little faith in America’s freedoms as to think them vulnerable to a few homicidal maniacs, egged on by his friends in the gun lobby? The answer is that they have been conditioned to fear.

Of course not all Americans agree with Trump and not all Britons agree with Cameron and Benn. But then not all Muslims agreed with Bin Laden or sympathise with Isis. The glib association of broad groups with extremist ideologies is the first step away from democracy down the ruinous road to paranoia and division.

There is now a copious literature on Isis. Books by Patrick Cockburn and the Guardian’s Jason Burke, and a searing analysis of the Raqqa caliphate by Graeme Wood in March’s Atlantic magazine all tell the same tale: of ham-fisted interventions, poor intelligence, counterproductive assassinations and the misjudgment alike of friends and enemies. It is a story of predictable consequences claimed as “unintended”.

Al-Qaida in 2001 was a tiny cell in an Afghan mountain. By overreacting, the west turned it into a global force. It proceeded to sow anarchy across Afghanistan and Iraq and then attempted, after 2012, to destabilise President Assad in Syria. This compounded the foolishness, finally creating a vacuum in which an Isis caliphate could take root. It is, as Wood emphasises, a different theology and different methodology from al-Qaida, a state not a cell.

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There can be no argument. Britain was in part responsible for the creation of Isis. Now Cameron appears to believe that it can be bombed into defeat, repeating the oldest military fallacy, that bombers win wars. From all I have read, Isis will never surrender to bombs. It is the purest of hieratic regimes. It might be wiped out with appalling slaughter on the ground, but then what? For the present it can probably best be contained by surrounding forces in the Sunni triangle, where it should ultimately rot from its internal contradictions.

Meanwhile, western liberal democracy is threatened not by a caliphate or “radical Islam” but by itself. Fear is so prevalent a form of politics because it is the cheapest. That is why inducing politicians and the media to spread fear is the terrorist’s most potent weapon. As in judo, it is the weak exploiting the strength of the strong to defeat him.

Islamist terrorism does not seek the conversion of the west to Islam. It is not stupid. Bin Laden’s objective was to show Muslims that the west’s claims to moral superiority were a sham. So-called liberal values could be undermined by turning western leaders into bigots, paranoid warmongers and oppressors, especially of Muslims. Bin Laden sought to contrast the steadfastness of conservative Islam with the hypocrisy and degeneracy of a frightened west. He has had a pretty good month.

Every religion has its fundamentalist strain. Liberal democracy should not give it a megaphone, but defeat it with moderation and reason. Yet as Trump grovelled before the shades of Bin Laden this week, all I could hear was a voice from a watery grave crying, “Attaboy, Donald! Keep it up. God is great.”