As horrified members of the Establishment on both sides of the Atlantic struggled to come to terms with the prospect of President Donald Trump, the British Foreign Secretary had a message for his “beloved European friends and colleagues”:

“I think it’s time we snapped out of the general doom and gloom about the result of this election and the collective whinge-arama that seems to be going on in some places.”

One of Boris Johnson’s strengths, displayed both in his journalism and in his politics, is the speed with which he reacts to a moving story. He saw that refusing to accept Trump’s victory would be the height of stupidity.

By coining a term unknown to diplomacy – whinge-arama – and refusing to attend yesterday’s special EU meeting to discuss Trump’s victory, Johnson advertised the British Government’s welcome to the President elect.

He had himself been extremely rude about Trump in the past, as when he remarked that “Donald Trump is clearly out of his mind”.

But times have changed, and Johnson now points out that Trump “wants to do a free trade deal” with us, which is “a great opportunity”.

The possibilities are not, however, all good. As Paul Goodman pointed out yesterday, Trump has cast the future of NATO into doubt. If isolationism triumphs in Washington, we could soon find ourselves needing to construct a new, European system of collective security.

Foreign policy experts have cautioned in recent days that strategic differences between Europe and the United States could widen as a result of Trump’s victory.

So Johnson finds himself at the centre of events, which is exactly where he likes to be. He is deeply involved both in Brexit and in the linked question of how to handle Trump.

The temptation presents itself to make an audacious bid to elbow Nigel Farage aside, and become Trump’s best friend in Britain.

When Harold Macmillan was Minister Resident at Allied Forces HQ in Algiers during the Second World War, he would describe to new arrivals from London, such as Richard Crossman, how to deal with the Americans, who under General Eisenhower were in overall command of the Anglo-American forces:

“We, my dear Crossman, are Greeks in this American empire. You will find the Americans much as the Greeks found the Romans – great big, vulgar, bustling people, more vigorous than we are and also more idle, with more unspoiled virtues but also more corrupt. We must run AFHQ as the Greek slaves ran the operations of the Emperor Claudius.”

Johnson will be well aware of this vainglorious analogy, made by his fellow classicist and Balliol man. One hopes he will also bear in mind the enthusiasm with which the Americans helped to wind up the British Empire.

The Foreign Secretary revels in uncertainty. As he himself once told an interviewer,

“There comes a point when you’ve got to put the dynamite under your own tram tracks…derail yourself. See what happens.”

His whole life has been a preparation for being unprepared. So at a time when scant preparation has been made for Trump’s presidency or indeed for Brexit, and foreign policy cannot consist of business as usual, his temperament might be thought to suit him to be Foreign Secretary.

Foreign policy experts tend, however, to find him a reprehensible figure. One former diplomat, whom I had always imagined to be a man of peace, said of Johnson, “I’d push him off his bike if I saw him in the street.”

The experts (at least those who have not actually worked with him) accuse him of “lack of self-discipline”,  “lack of content in his vapid assurances”, “insistence on seeing foreigners as raw material for jokes”, “the belief that he can bullshit because he’s very bright”, and “the height of irresponsibility for drawing up no plan for Brexit”.

To them, he is the British version of Trump. Johnson has long been scorned by his opponents as a clown, but now they hate him for having persuaded the British people to vote No.

In some ways, this is to Johnson’s advantage. He is underestimated by his critics. They are determined to see him as flippant, unreliable and incompetent.

But it makes writing about him rather difficult. For as soon as one suggests that this priggish, pedantic, hysterical onslaught on him is absurdly overdone, and he has the potential to become a great Foreign Secretary, one is liable to be dismissed as a mere apologist.

While working on the first and most frivolous biography of him, Boris: The Adventures of Boris Johnson  – just updated to include the drama of the referendum and the 20 stirring days in which Theresa May became Prime Minister and Johnson Foreign Secretary – I took care to include the evidence one would need to make the case both for and against him.

When the book first came out, Johnson described it in a genial tone as “rubbish”, a verdict with which Michael Gove now concurs. It is heartening to find they can agree on something.

The much wider question is whether as Foreign Secretary Johnson can win the respect of his critics. And here James Landale, diplomatic correspondent of the BBC, points to the possibility that Johnson’s friends, or colleagues, could be more subversive than his enemies:

“Now every government has a court jester and Boris Johnson will never be able to escape that title. But his role in this government is crucial. He is there to convince the international community that Britain is not turning its back on the world post Brexit, that Britain has a positive role to play in global affairs.

“And to do that he needs to be taken seriously. Many foreign politicians and diplomats that I speak to tell me they are pleasantly surprised when they meet the Foreign Secretary for the first time.

“They talk of the man behind the caricature – the cultured, over-educated intellectual who often speaks a bit of their language and who can be thoughtful when he is not gripped by banter.

“The problem is that many others – who have not met the Foreign Secretary in person – often still see him as a kind of upmarket Nigel Farage, a Eurosceptic clown with clout.

“So to do his job, Britain’s diplomat-in-chief needs every bit of credibility he can lay his hands on. He is already the butt of many jokes. The last thing he needs is his prime minister adding to the mirth.”

That was written after Johnson accepted an award from the Spectator. He diminished the envy people might feel of him by comparing himself – with characteristically exaggerated self-deprecation – to Michael Heseltine’s Alsatian dog, whose life had unexpectedly been spared, though only for a day.

The Prime Minister seized the chance to remind him: “Boris, the dog was put down…when its master decided it wasn’t needed any more.”

All very funny, and appropriate to the occasion, but can diplomacy be conducted in this style? Ten days ago, Johnson visited his German opposite number, Frank-Walter Steinmeier, in Berlin.

The BBC asked Steinmeier: “I wonder, are you running out of patience with Britain?”

Johnson interjected: “He’s not running out of patience, I can tell you.” This sounded wrong, at once impertinent and defensive, for as Steinmeier himself avowed, he was “not particularly amused” by Johnson’s decision to back Brexit.

Members of the British foreign policy Establishment reckon Johnson “has not got room for buffoonery now”, and warn that he has “not got much leeway with quite a large group of people”.

Jonathan Powell, who was Tony Blair’s chief of staff, observed after the American presidential election that Donald Trump’s use of “conciliatory words” is “a bit like listening to Boris Johnson trying to be serious – it’s not really very convincing”.

Such condescending dismissiveness is widespread among the chattering classes. But it says more about them than it does about Johnson. If they could bring themselves to look at him in a fair-minded way, they would admit he is a humane practitioner of the long-established though always evolving tradition of British politics. They should be giving thanks that Brexit is in the hands of such a liberal-minded Conservative.

“I’m sure Boris doesn’t want to change his style,” one elder statesman said, “and I’m sure he knows he has to do it.”

His habitual style, both in politics and in journalism, is to handle some grave theme in so light a manner that it does not weigh on the spirits of his audience. Comedy is placed at the service of a message which could be stated in its baldest form in a sentence or two, and is usually rather serious.

Having reread many of his articles, I can confirm that very few of of them fail to make some thoughtful point, but that he has a compulsion to conceal the seriousness of his intent.

As Gove once put it in a “Portrait” written for a collection of Johnson’s journalism: “The use of laughter as a tool of political seduction is the quintessential Johnson manoeuvre.”

So successful, or over-successful, is this Wodehousian camouflage that he is still widely seen as a Bertie Wooster figure. That is how he sounded in Michael & Boris: The Two Brexiteers, a radio play by David Morley broadcast on Wednesday of last week, with Alistair McGowan playing Johnson, and Gove portrayed as a disloyal version of Jeeves.

Though capable of adapting his tone, learning from setbacks, and indeed preserving a diplomatic silence and veiling his intentions, Johnson is quite unfitted to adapt his style in order to become, in T.S. Eliot’s words,

…an attendant lord, one that will do

To swell a progress, start a scene or two,

Advise the prince; no doubt, an easy tool,

Deferential, glad to be of use, 

Politic, cautious, and meticulous;

Full of high sentence, but a bit obtuse…

He will never subside for very long into the monstrous verbiage, an affront to the wider public, in which foreign affairs are discussed by conventionally serious people.

And where did wooing the Germans get David Cameron? For much of his Bloomberg speech, the then Prime Minister gazed directly at the German ambassador, whose approval clearly meant much to him.

Cameron took enormous trouble, via Ed Llewellyn, to avoid offending Berlin by demanding too much, but in the end Angela Merkel was nothing like as helpful as the British had hoped. The dreary old EU orthodoxies – the kind of thing Johnson has scoffed at for decades – reasserted themselves, including a lot of pious and inflexible guff about the “four freedoms”, along with no sympathy for the national freedom to control one’s own borders.

Johnson is now in charge of a department which has suffered, with the popular vote to leave the EU, the most crushing blow to its world view and self-esteem since Sir Anthony Eden cut the Foreign Office out of his secret diplomacy and launched the Suez venture.

On Johnson’s first day at the office, he addressed the entire staff. He was then asked what lunch he would like to be brought to him in his grandiose room. He went instead to the canteen, a practice he has continued since, and which people really notice. Hierarchy is tempered by camaraderie.

Vast quantities of paper descend on a Foreign Secretary, but Johnson calls in the officials who produce the paper and talks to them. He wants the people who work for him to enjoy themselves: an instinct which not all ministers possess, or are capable of showing.

As one official puts it, “The Foreign Office is like a labrador. If you show it a bit of love, it will be eternally loyal. And Boris has tickled its tummy very well.”

At the Conservative Party Conference, he delivered one of the few speeches worth listening to (here is the YouTube version), a grand survey of European history since the fall of the Berlin Wall, which began with a comic account of being told by his Russian opposite number: “It was you guys who imposed democracy on us in 1990.”

The Foreign Secretary went on to insist (a frequent refrain) that “we are not leaving Europe”, and delivered a paean of praise to Britain as a “soft power superpower”, which went down so well that he elicited a cheer from the Conservatives in Birmingham for the BBC as “the single greatest and most effective ambassador for our culture and our values”.

When Michael Cockerell profiled the Foreign Office, he interviewed Lord Renwick (Diplomatic Service 1963-95), who observed: “The toughest negotiations any Foreign Secretary has are always with his own Prime Minister.”

Prime Ministers generally prefer to run foreign policy from Number Ten: one thinks not only of Eden but of Margaret Thatcher and Tony Blair.

On Brexit, this will undoubtedly be true of May, and David Davis will be determined to play his part too, as will Liam Fox. But if I were working in the Foreign Office, I think I would reckon that Johnson, with his irrepressible urge to be in the thick of it, has a better chance than some quieter, more diplomatic figure of averting the department’s marginalisation.

Johnson’s mortal weakness in the recent leadership contest was that he failed to inspire trust, even from Gove, his companion in arms during the referendum. May won because she was seen as the most trustworthy candidate: a function above all of her steadiness as Home Secretary.

Can Johnson establish a similar record as Foreign Secretary? In order to carry out that job successfully, he will need to do so. Brexit depends on British ministers being seen as trustworthy, for only then can durable agreements be reached. As Talleyrand, one of the most brilliant of all diplomatists though not himself a byword for fidelity, put it at the end of his life:

“Here there is one thing that I must say, in order to destroy a widely spread prejudice: no, diplomacy is not a science of deceit and duplicity. If good faith is necessary anywhere it is above all in political transactions, for it is that which makes them firm and lasting.”