Had president Trump any sense of history, he might well be aware that the Darroch affair – as it may yet come to be called and which has now led, desparately sadly in my view, to the resignation of a hugely respected and distinguished diplomat – is by no means the first time that a transatlantic ambassador has given advice not to the liking of his hosts.

In the dark days of 1940, the then-United States ambassador to the United Kingdom – one Joseph Kennedy, an extremely wealthy businessman and investor and the father of the Kennedy clan of John, Robert and Edward – repeatedly advised the then-president Roosevelt not to provide military and economic assistance to the UK on the grounds that the war against Nazi Germany was already irretrievably lost. Shortly after leaving his post in the autumn of 194,0 he famously told the Boston Globe in an interview that “democracy is finished in England”.

Fortunately for us all he was wrong and, equally fortunately, Roosevelt rejected his advice and provided the assistance that he had counselled so strongly against. But there are perhaps lessons from the Joseph Kennedy story that are relevant today.

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The first is that ambassadors may be right and they may be wrong. They sit in the capitals of their host countries and they form views about them. But they are not some form of divine soothsayers. Just as Kennedy was so fundamentally and notoriously wrong in 1940, so Sir Kim Darroch may be wrong today in some of the judgements he has reached.

But the second and more important point is that telling it as they see it is their overriding responsibility; if they do not do that then by definition they have no value. Clearly it is deeply embarrassing if their views get leaked but that does not mean that, somehow, they should not have given them to their governments in the first place.

The third key point is that it is up to their governments to decide how much weight to give to those views. Fortunately for us, and for the United Sates, Roosevelt in 1940 decided to ignore the advice he was getting from his ambassador in London. For our part, we simply do not know how much weight the current foreign secretary and prime minister have given to the advice they have received from Sir Kim Darroch. It will no doubt have been one piece of advice amongst many from other sources. But the key point is that it is in the end simply advice.

I do not detect that history "BT" (Before Trump) is president Trump’s strong suit. His version of American history seems based on the belief that before his coming, all was disaster, but that since his inauguration, America has entered a golden age. But if he had even a shred of historical perspective, he might have seen the Darroch affair for what it should have been: a storm in an embassy teacup which, had he chosen simply to rise above it without comment, would quickly have disappeared with the tea leaves down the embassy drains. Instead his petulant and quasi-hysterical reaction has served only to prove the Darroch hypothesis.

And the reaction of our own government? Not for the first time, Theresa May has kept her own counsel, made clear her support for Sir Kim but otherwise resisted the temptation to lock public horns with Trump. As his reaction has diminished him, so hers has dignified her. But, of course, she will be gone from No.10 within weeks. Perhaps the real lessons to be drawn from the Darroch affair are the reactions of those who are bidding to replace her. I have a sense that if president Roosevelt were alive today and surveying the responses in London to president Trump’s tweets from the Conservative leadership candidates – or in the case of one candidate, the lack of response – he might contrast them sharply with the statesmanship on this side of the Atlantic which he would remember from his own era as president.

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