It is not often, especially in the midst of what has been a grimly dreadful election campaign for her, that one feels some measure of pity for Theresa May. But there she was today, gamely putting on her bravest, gamest, face when she was asked for her reaction to Donald Trump’s latest witless provocations.

The American president, you can hardly failed to have noticed, has not covered himself in glory since the weekend’s terrorist attack in London. When the city’s mayor, Sadiq Khan, suggested that Londoners should not be alarmed by the deployment of additional armed officers on the streets of London, Trump blustered “At least 7 dead and 48 wounded in terror attack and Mayor of London says there is ‘no reason to be alarmed!’”

Well, indeed there wasn’t though you wouldn’t expect him to know that. Undeterred, Trump returned to his phone this morning to suggest that Khan was failing in his duties (Trump should know a thing or to about that, admittedly). 'Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his ‘no reason to be alarmed’ statement. MSM is working hard to sell it!'

Here, at last, is something all Brits of sound mind can agree on: Trump can jog on.

Alas, the Prime Minister finds herself in a different situation. Her decision to cuddle the Donald in the first weeks of his presidency looked foolhardy at the time and nothing that has happened since has done anything to make it look any better. The days when Britain’s conservative press salivated over the UK being 'first in line' for a post-Brexit free-trade agreement with the United States seem to belong to a different, bygone, era. Those people confidently boasting that President Trump would be good for Britain have fallen oddly silent.

Realpolitik is realpolitik and everyone understands that. But it’s a grubby business, nonetheless. So you can understand why so many people would like Theresa May to set about Donald Trump today. Indeed, she was thrice given the opportunity to do so. The Financial Times, Buzzfeed and Bloomberg each asked for her reaction to Trump’s tweets and each time she declined to answer the specifics of the questions asked her.

Everyone knows why this is and it’s not because Theresa May is a coward or some other guff. We know that Trump can only cope with unctuous flattery and that, satisfying as it may be to criticise him, doing so isn’t likely to advance the UK’s interests vis a vis its relationship with the United States.

So Mrs May says nothing, even though saying nothing makes her look terrible. This is no time for a showboating Prime Minister, she might say, and she might have half a point. But it still looks weak and miserable and craven and all kinds of rotten.

The telling thing, however, is not May’s timidity but, rather, the manner in which the British government now speaks about the American government. For it is now clear that Trump is, at best, an unreliable friend and even, perhaps, a kind of 'frenemy'. We have to try to do some business with him but we will do so while holding our nose.

This is Trump’s extraordinary achievement: he has put the United States into the same category as Saudi Arabia. Realpolitik demands that we treat the Saudis with more respect - and more politeness - than they deserve. Realpolitik means accepting that going out of our way to antagonise the Saudis, for all that they preside over one of the planet’s nastiest regimes and societies, is not in our own best interests. This, it is true, is something of which the Saudis remind us all the time, using their own failures as a form of geopolitical blackmail. If you dislike us now, they say, wait until you see what would follow us.

There is much that is miserable about this but while there is undoubtedly something abject about the manner in which we play nice with the Saudis, you can also make a plausible argument that, on balance, doing so serves the national interest better than would more morally-pleasing alternatives. You do what you can, where you can, when you can but you also know this is usually going to be less than you might like to do, if the world were ordered differently and more conveniently.

Now, at least in terms of Prime Ministerial rhetoric, we treat the United States of America in much the same way. We must watch what we say, lest the truth of what we think be let loose upon the world. Friends speak candidly to friends, we say, but such rules no longer apply in the age of Trump. And if that means keeping quiet even when he interferes in our own politics then, hard as it is to swallow, we still swallow our tongues. Because that’s what the interests of the state demand.

I think it’s possible to sympathise with this view even while regretting it. It would, you think, give Mrs May some satisfaction to let Donald Trump know how a 'bloody difficult woman' reacts to his bovine interventions.

But, in the end, that she does not do so tells us more about Donald Trump than it does about Theresa May. It tells us that he has disgraced the United States to the point at which some truths cannot be said in polite - that is to say, public - society. Instead we kid ourselves that everything is fine and trust that no-one will care to recall the manner in which raison d’etat demands a degree of self-abasement. Hypocrisy, after all, is diplomacy by another name.

In that respect, Washington is now Riyadh on the Potomac. Which, when you think about it, is an extraordinary, appalling, development. Eventually however, even realpolitik reaches a snapping point; at some point, the Prime Minister will have to decide if being studiously polite - or as polite as possible - to and about the American president is worth the damage that reticence does to her own reputation. The country can accept a lot but there’s still a limit, you know.