The powerlessness of Donald Trump is a well-kept secret. He distracts attention from it by his limitless vulgarity. His game, which he plays with pernicious glee, is to drive members of the American establishment so mad with pain and embarrassment they cannot stop themselves crying out.

Their shrieks of agony convince Trump’s working-class supporters that he must be doing something right, and is taking revenge on all the stuck-up, moralising types who despise them and want to impose a tyranny of liberal virtue on parts of American society which were never liberal. He also provides a lot of entertainment for people who are not exactly his supporters, but find him an amusingly implausible figure.

As on a successful reality TV show, there is always something freakish going on at the Trump White House, or whichever golf club has been pressed into service as his summer quarters. The bizarre and unpredictable nature of the show makes it watchable. Americans love a performance, the more exaggerated the better, and so do people on this side of the Atlantic.

I have just spent three weeks in the United States, and since getting back I have found a surprising number of people break into a smile when I say I have been in the land of Donald Trump.

This frivolous response drives serious-minded American liberals even madder. Their inability to relax, and form a true estimate of their opponent, is one reason why he became President and Hillary Clinton did not.

To have such an untrustworthy braggart playing the role once graced by George Washington and Abraham Lincoln is no laughing matter. It is a national humiliation.

But Trump neither knows how the American government works, nor possesses the time and ability to learn. He is a less benevolent version of the Wizard of Oz: a bluffer who is bound before long to be found out.

His dealings with just about every other part of the republic have been pitifully inept, and serve to show how impotent he is. At frequent intervals, he sacks various people he has just appointed, or else precipitates their resignations.

He also insults the very members of Congress whose support he needs to get any serious measure through. He is at least as much of an embarrassment to Republicans as to Democrats.

Trump is now the prisoner of the last people he has appointed. Hence his subservience in recent days to the establishment’s line on Afghanistan. For if he loses another set of staff, who of any weight will he find to replace them?

There is a lesson here for the British Government. There is always a danger the British Prime Minister, suffering from an acute inferiority complex induced by contemplating the vastly greater power of the United States, will display a kind of abject sycophancy towards whoever happens to be President.

Margaret Thatcher avoided this with Ronald Reagan: when necessary, she had arguments with him. But Tony Blair did not avoid it with either Bill Clinton or George W. Bush: he sucked up to them in a most shameless fashion.

Theresa May began by displaying a somewhat imprudent keenness to become better acquainted with Trump. This must now cease. Britain has everything to gain from maintaining the close and cordial relations with the Washington establishment which have existed, with one or two bumps, since 1941. But we have no interest whatever in standing by a bounder who is in the process of destroying himself.