Boris Johnson has always been a clown – but he's becoming a dangerous one

If Theresa May handed Boris Johnson the Foreign Office with the Machiavellian aim of neutering any threat he posed by having him fail, she must be delighted with the result.

It seems that wherever he goes he leaves a trail of devastation behind him. Yet Mr Johnson has survived because he is one of those politicians who has the ability to get away with things that would have long ago doomed less charismatic and media-savvy performers. All it takes is a self-deprecating smile and an insouciant shrug and he's out of jail.

Mr Johnson's history is littered with such incidents, going back to when he infamously discussed having violence inflicted upon a journalist critical of his convicted fraudster friend Darius Guppy.

In the years following that ugly episode, he has insulted more world leaders than his boss Ms May has probably had the chance to meet, and as Foreign Secretary seems allergic to performing any diplomatic function without first putting his foot in his mouth.

Little wonder, then, that this week has seen him describe the Labour leader Jeremy Corbyn as a “mutton-headed old mugwump” in a newspaper column.

The word sounds like one of JK Rowling’s fantastic beasts, although she actually borrowed it to describe the head of her wizarding court.

On those rare occasions it finds its way into less magical modern English, it is used to refer to someone who is aloof or independent, especially from party politics. Mr Corbyn has made a virtue of his independence from the establishment, and his disdain for political convention. Coming from the likes of Mr Johnson, it is not impossible that he could consider it a back-handed compliment.

If the jibe was intended to be funny, however, it was humour only of the lowest kind.

Mr Johnson’s act is starting to wear thin. That was made all too clear by his following the column with yet another ill-advised belly flop onto the foreign policy stage.

Britain, he said, would immediately agree to a request from Donald Trump to join military action against the Syrian regime of Bashar al-Assad, without first seeking approval from the House of Commons. The failure to secure it stymied the ambitions of his former friend David Cameron to join an earlier US-led intervention.

The irony of perhaps the most high-profile backer of Brexit cavalierly proposing to sacrifice its armed forces on the altar of becoming Mr Trump’s poodle is a rich one. This hardly smacks of backing “independence” for the nation.

Brexit was claimed to be about restoring Britain’s – and Westminster’s – power to make its own laws and policy. Instead, Mr Johnson’s words imply that he would be willing to hand it over to the White House along with a blank cheque, bypassing the House of Commons in the process. Parliament, it seems, isn’t as sovereign as we have been led to believe.

If Ms May’s aim in making Mr Johnson Foreign Secretary was to expose his failings, she has been more successful than even she could have imagined.

At some point, however, she will have to face the up to the truth that Mr Johnson is rapidly reaching his sell-by date. He has always been a clown. He is becoming an increasingly dangerous one.