Sunday provides a moment for reflection. I admit to having a more troubled state of mind this week than last. I thought Trump would win the election then, but could hope I was wrong. It turned out I was not. President Trump is on his way. Some, I am sure, view the prospect with equanimity. Many more, I suspect, will not.
Let me ignore the impact of this decision on the USA for the moment: they at least can blame themselves for it. Let me instead consider the consequences for the UK, because these are serious.
Some assumptions have to be made explicit. The first of these is that by itself the UK is a fairly insignificant power. Declining economically and militarily ill-equipped, as well as poorly judged, we cannot any longer pretend we are a world power. We might have been. We are not now.
Second, the US is moving to economic and military isolationism, which has in modern history been a move with few recorded successful consequences.
Third, this will leave a power vacuum on which we alone will have no influence. It is, however, a situation where Europe might provide the necessary counter-balance to both China economically and Russia militarily.
Fourth, without that counter-balance the world is a more dangerous place in almost every way we can think of. I wish it were otherwise, but I am not naive.
So, fifth, if peace is to be maintained (and I think that the highest duty) when the US is threatening to undermine NATO Europe has a new and essential role.
Those are the assumptions. What then are the conclusions? There is only one, and it is that, like it or not, the UK's only partner of consequence in the real world is Europe. Face reality: the US has now turned its back on us. May came ninth on Trump's call list. The special relationship is dead. We are now stuck with geography alone, and that means we only have Europe.
And we have turned our back on Europe. So we are now alone, which is a pretty uncomfortable place to be.
This then demands a serious reconsideration of policy in the light of changed circumstances. When the facts change (and Trump has undoubtedly changed the facts) then opinion has to change too. In this case that means that because there is no prospect of us changing Trump's mind we have to re-examine the decision we have made to leave Europe. Nothing else makes sense.
A wise prime minister would now present these facts to the country. Instead we have a foreign minister who has today declined to join EU foreign ministers in considering the issue of how to manage the challenges that Trump's election poses. And as acts of folly go, that's pretty big. Ignore the economics: this is about security. And we have a government that will even put that on the line for the sake of dogma now.