When I saw the closeup of Donald Trump’s weak orange hand pressed into Theresa May’s cold, white one, I understood what Britain has become. Not so much Little Britain as Lost Britain.

She had gone to Washington to salvage the “special relationship”, weeks after the true special relationship – between Trump and Nigel Farage – was proclaimed. What she found was a man committed to destroying the global order but who may be frightened of stairs.

Consider the topography of the new global situation: a multilateral system, based on global institutions that functioned badly, is becoming a great power system in which global institutions will be paralysed.

It does not matter that Republican-drafted legislation to pull the US out of the United Nations is a gesture: “America first” means what it says. The US designed globalisation, benefited massively from it and imposed it through the twin methods of commercial dominance and military supremacy. Now it is determined to walk away from globalisation, and on its own terms.

The Iranian scientists, the Oscar winners and the Syrian refugees turned away from US airports this weekend were meant to symbolise the break.

That is bad for America – but truly catastrophic for the UK. The British political class now finds itself in a situation with no modern precedent. Instead of being the US’s junior partner in an American-administered multilateral system, it is being forced to take sides, curry favours and destroy decades of economic and diplomatic goodwill.

In the great power system, you grab what you can within roughly defined spheres of influence. Syria is in Vladimir Putin’s sphere of influence and so its democrats and its intellectuals must not only suffer defeat, but a defeat reinforced by Trump’s ban on them moving to or even visiting the US.

Britain lies within the US’s sphere of influence. And May last week found out what that means.

For Trump, Britain is a tool to break up the European Union. When he predicts the EU’s demise and promises Britain a trade deal designed to destroy 30 years of economic ties with Europe, the entire British political elite has to understand how relentlessly it is being played.

It’s the same game with Nato. The British military has, for practical and historic reasons, moulded its force structure to provide a sharp edge to the US’s blunt but heavy weapon.

But Trump regards the Nato mutual defence commitment as a mere suggestion, not a treaty obligation. It will be honoured where it suits his great power method – of granting favours and issuing threats to subordinate powers; but no longer will it sit as an absolute guarantee.

Putin does not intend to attack Europe, merely to demonstrate he has the ability to do so and the will, if needed. What he wants is more coastline along the north of the Black Sea, and the paralysis of Nato’s willpower in the Baltic.

We do not know what May discussed with Trump but, given the presence of their national security advisers, alongside people with no qualifications for running major states, it had to have been: how do we simultaneously contain and appease Putin?

May has revealed nothing of what was decided, but her first action was to sign an arms deal with the nascent dictator Tayyip Erdoğan. Her second action was to endorse, by her initial silence over the Muslim travel ban, the division of the Islamic world into “friendly” and “unfriendly” countries.

The number one unfriendly country is now Iran, which we – as part of the EU – helped sign a strategic peace with just 19 months ago. The friendlies – Turkey, Egypt and Saudi Arabia – are exactly the ones you need if you have ceded the division of the world into spheres of influence.

We have two choices: we can acquiesce and let this sociopathic sex pest grab our collective hand amid the scary world he has created. We can abase ourselves for special favours – such as exemption for British dual nationals. Or we can reject Trump in his entirety.

Just as Trump is meddling – via Ukip – in the racial politics of Britain, British liberalism and socialism has the duty now to intervene in the social politics of the US. We must bet on Trump’s defeat in 2020, help train and fund lawyers and journalists to hold him in check, and – once he is gone – attempt to rebuild the multilateral order. Yes, and ruin his state visit: through all forms of protest legally possible.

The shape of a Dump Trump foreign policy is clear: Britain must strengthen its alliance with countries whose governments and peoples share our values: France, the Netherlands, Germany, Canada and Greece. Although we are headed out of the EU, the case for the softest possible form of Brexit is only strengthened by the US’s descent into arbitrary government.

And we should ringfence Britain’s armed forces from inter-operation with a US military should it recommit to the use of torture in war.

We should maintain sanctions against Russia, even as Trump tries to dump them. We should promote democracy and human rights in Russia, even as his state department becomes the first since 1945 to leave Russian dissidents in the lurch.

May will do none of this. Her entourage is full of political nondescripts: suburban power-worshippers from the Tory shires, adrift like her in this new and dangerous situation.

May showed her true instincts this weekend. If followed to their logical conclusions, she will help Trump destroy Europe in return for a trade deal that will then destroy the NHS.

But at least Trump was elected. May was not. Now would be a great time to measure whether the British people really do consent to hard Brexit and hard racism.