One of the curious side-effects of the Trump crisis, here in liberal America, has been the near-disappearance of the individual perspective. Nobody is in possession of insights or facts that everyone else isn’t also in possession of.

We all absorb the same breaking news, the same analyses, the same comments and jokes and memes. Our outrage, horror and anxiety duplicates the outrage, horror and anxiety of the next guy. To say that we’re all on the same page, politically and psychologically, would be an understatement. We’re photocopies of one another. Our blind spots are identical.

Something similar seems to have happened in Brexiting Britain. A format of preoccupations and emotions, shaped back in 2015, still exerts control. This might explain why a fact that’s obvious, from an American perch, apparently has escaped the notice of a lot of Britons and their parliamentarians. As they argue with Lilliputian ferocity about hypothetical trading scenarios and legislative technicalities and putative “deals”, the UK faces its gravest national security threat since the second world war. The threat comes from here, the United States.

To be succinct: President Trump, animated by private motives as yet undisclosed, wants to bring about a Russian-American axis that would enfeeble Nato, destroy the European Union and dominate a continent reduced to politically dysfunctional national fragments. This isn’t speculation. European leaders in Malta last week discussed precisely this new state of affairs.

There is a global threat as well as a European one. Operating under the “America first” rubric, Donald Trump has instantly turned the US into a rogue state. Internationally agreed rules on trade, territories, refugees, climate and disarmament are, it seems, to be treated as no longer binding on America.

The president’s sudden, vicious restriction on Muslim immigration; his harassment and insulting of the Australian and Mexican leaders; his erasure of all reference to the Jewish genocide in his remarks for International Holocaust Remembrance Day; his appointment of his senior political adviser, the apocalyptic ethno-nationalist Steve Bannon to the National Security Council: it all adds up to an agenda of unhinged Christianic belligerence and international lawlessness. And that’s without even getting into the most dangerous issues of all: Iran, China and Trump’s questionable mental instability.

To make matters worse, Trump rejects any kind of institutional control. He has shrunk the executive branch of government into a private dictatorial clique. He has excluded from his decision-making process the cabinet secretaries, civil servants and members of Congress who would ordinarily be consulted. The intelligence agencies have been marginalised, and the White House record-keeping rules ignored. Trump has ridiculed journalists, judges, protesters, senators, ethicists, spies, diplomats, chief executives, Oscar winners and Arnold Schwarzenegger. He daily undermines the very idea of objective truth. If the Richter magnitude scale were applicable to the terajoules of dictatorial seismicity, Trump would register as a six.

Trump with Steve Bannon (right) and Jared Kushner, Trump’s son-in-law, during a swearing in ceremony at the White House: ‘It all adds up to an agenda of unhinged Christianic belligerence and international lawlessness.’ Photograph: Carlos Barria/Reuters

Simply to recapitulate these facts is to experience staleness, exhaustion, banality, fear, denial – as if they were unwelcome test results just reported by one’s doctor.

But there can be no question of living with this pathogen. Trumpism is a lethal, highly infectious political disease that attacks liberal democracy wherever it finds it. Either you fight it or you succumb to it. Which brings us back to Brexit.

The referendum, and the debates animating it, took place in a world that simply no longer exists. In early 2016 few seriously reckoned with the possibility that Donald J Trump, perhaps the most ludicrous of the Republican primary contestants, would end up occupying the White House. If they did reckon with it, nobody foresaw the presidency that we now have. Everybody assumed that, if Brexit came to pass, the United Kingdom would negotiate its new trade and security arrangements in a geopolitically stable world. Everybody assumed the presence of a sane and friendly American president loyal to the Atlantic alliance and its shared liberal democratic values. All these assumptions, so basic they were never even discussed, have turned out to be false.

And yet the Brexit white paper, published last week, makes no reference to the changed circumstances. The only reference to Trump is indirect: “The new United States administration, the world’s biggest economy, has said that they are interested in an early trade agreement with the UK.” The grammatical chaos of this sentence reflects a broader confusion. The white paper recognises that Brexit has huge security implications. But, incredibly, it states: “The Government’s national security strategy established clear national security objectives. The 2015 Strategic Defence and Security Review (SDSR) set out a funded plan to achieve them and we are now focused on delivering that plan.”

That’s right: the UK’s current national security plans are the security plans made back in 2015. WTF, if I may put it that way. The SDSR was based on the National Security Risk Assessment of 2015. That assessment states, quite rightly: “Our democratic and inclusive values are the foundation of our security and prosperity. We will continue to uphold these values against those who are intent on undermining them.” No doubt written with Islamic extremism in mind, these words are, two years on, applicable above all to Trump.

It all puts the British government in a terrible position. In order to get the post-Brexit trade deal that the UK needs from the US, Theresa May will be forced to align Britain geopolitically with Trump, because Trump doesn’t do compromise. It’s either his deal or no deal. You’re either totally with him or totally against him. May will have no choice but to enable Trump’s ongoing attack on the very “democratic and inclusive values” that are, by the government’s own assertion, the foundation of UK security.

I’m not suggesting that the Brexit decision or parliament’s vote be revisited. I’m suggesting that if article 50 notification is given next month, as currently envisaged, the UK will be forced to choose between two options, both catastrophic to its national security. Either the UK makes common cause with Europe in its existential opposition to the Trump-Putin axis, in which case the UK will end up with no trade deal from the US, its biggest single trading partner; or Britain will make that trade deal, but will become Trumpist America’s client state, because to oppose the president or his great friend Vladimir Putin would put at risk the trade deal.

Fortunately, there is an alternative to this lose-lose scenario: adhere to the Brexit decision, but suspend article 50 notification until it is clear that the national security crisis has passed. The UK and its European friends would stand together against Trump in their joint hour of need. Moreover, a Europe united in opposition to Trump would be a very grave blow to the despot. Americans have their own vision of their national security, shared by almost everyone across the ideological spectrum. It does not involve befriending Putin’s Russia at the expense of old European allies, the UK in particular. If Britain makes the right decision, it will be Trump who is placed in an impossible position.

To suspend article 50 notification – or to suspend negotiations with the EU after notification – would require courage. Trump would be foiled and therefore angered, and no doubt there would be a lot of complaining in the UK. But surely national security is a non-partisan, non-negotiable, irreducible issue. With clear political leadership, people would get it very quickly: this is 2017, not 2015; Trump is a much bigger, much more immediate threat than the EU: deckchairs, Titanic. Once the Trump threat has passed, EU withdrawal will still be there, waiting to be triggered or negotiated. The trick is to ensure that a recognisable UK will be there too.