The most significant number in America this week is not – not – the number of times President Trump “took” to Twitter to do something terrible. This week US growth in the third quarter was revised upwards. The US is on track to grow 3.3% this year. The economy is “juiced” as his fans say. The equities boom booms on. If it carries on like this he will get re-elected in 2020. Or there will be one of the most calamitous smashes on record, perhaps involving the simultaneous crash of China’s shadow banking system, that its desperate authorities are trying to clamp down on, and an American bust. If there is a domestic economic explosion, it will be hard even for Trumpists to make the case that he is a success.

Rather than waiting for the outcome, it is obviously much more fun to pay attention to Trump’s demented retweets of a far-right British group of losers. The retweets have provoked a diplomatic incident with the UK government partly because there is still something mesmerisingly awful, shocking indeed, that the country of Teddy Roosevelt, Coolidge, Truman and Reagan put this person in charge. One imagines Trump in their place in a bedroom in the White House, in the darkness in the dead of night, unable to sleep, his face illuminated by the glow of his phone, his frame hunched as he sits there reading about his favourite subject, himself, and sending out ridiculous messages against anyone who is critical of Trump.

Of course, it is shaming for a great country and troubling for the rest of us. Trump’s a narcissist who applies only one measure: is this person nice or nasty about Trump? Are they anti-Trump or pro-Trump? Me, me, me.

But while the dignified response of Theresa May and Tory ministers such as Sajid Javid and Sam Gyimah to his Britain First retweets has been on the money, some of the other responses by MPs have been cringe-inducing. Quentin Letts referred in the Mail to the scenes in the Commons when it was discussed as “the Outrage Olympics” – which is spot on.

There are serious policy implications that flow from the latest Trump Twitter row, however. When Trump became President, Theresa May rightly decided to be constructive and friendly. Trump likes Britain, or his golf courses in Britain, and wants to do something – trade – for the UK post-Brexit. The EU is an inexplicable concept as far as he’s concerned. Britain is leaving it. So he’ll want there to be some kind of deal, runs the logic of playing along.

The anger about Trump’s endorsement of British First underlines that it will be all but impossible for a British government to convince the public that any compromise – any compromise at all on standards and so on – is worth the price of a deal. The Tories have serious perception problems. Why make them worse by being seen as even remotely pro-Trump?

Although it was sensible to try – it usually is in diplomacy – it is very difficult to see the British government continuing the pursuit of the welcoming policy it has pursued this year. What’s the point when he’s so quixotic and unreliable? He’ll flip on the strength of a tweet or a stupid thing he misunderstood on TV.

This means the British government calculus has altered. The “working visit” Trump wants might not be possible. Diaries are filling up. Everyone here is very busy until, ooh, November 2020. Is that the time?

This cooling becomes a problem if Trump survives and even prospers, rolling on tweeting into a second term. But that’s something for May’s successor to worry about. All the evidence, anyway, is that if you need him he can start being nice again in thirty seconds if you say something – anything – nice about him. He is a narcissist, after all

And it is important to remember amid the hysteria of the moment that he will be gone eventually; that’s how it works in a two-term presidential system with checks and balances that may anyway bring down the curtain earlier. Afterwards the world will carry on, and at some point there will be a President of the United States who is not a man-child. There will be life after Trump, hopefully…