When, back in May this year, Donald Trump became the first sitting US President to visit the Western Wall, one of the holiest sites in Judaism, the Israelis were delighted.
The presidential visit, they said, implied recognition of Israeli sovereignty at the site.
They also thought it was a promising sign for them because most US presidents avoid making such a visit.
Well, there was nothing "implied" or "promising" about the announcement that President Trump is recognising Jerusalem as the capital of Israel.
That – and his order to move the US Embassy from Tel Aviv to Jerusalem – is nothing short of endorsement of Israel's annexation of the Old City back in 1967 after the Six Day War.
Now that is huge news for Israel largely because virtually every other nation has rejcted such a move in fairness to the Palestinians, who also claim the territory.
Traditionally, American presidents have viewed Jerusalem as the subject of negotiations with the Palestinians. But not this president, not Mr Trump.
The Israelis could not be happier. Well I guess they could be if they sensed some great national security strategy behind Mr Trump's move.
But if they look, I'm not sure they will find one. Neither will they find evidence of any long-held personal belief underpinning the decision.
No, like many of this president's decisions, it is born more of instinct and necessity than any thought-through strategic move.
The language he used in the White House when making the speech was very instructive if you're looking for reasons why Trump would risk sparking a major conflagration in the region.
He said that previous American presidents had failed to deliver on campaign promises to recognise Jerusalem as the capital of Israel. But, he added, "I have delivered!".
And delivery is what Trump is obsessing about at the moment.
He has no great domestic policy triumphs to his name, unless you count the economy's improvement as being down to him, which of course he and his supporters do.
But in campaign promises fulfilled, there are precious few.
So this could be done with the stroke of a presidential pen and a flourish. And so he has taken the opportunity.
With healthcare still stuck in the long grass, with the wall unbuilt and various immigration policies still bogged down in legal argument, he needs to tick some boxes.
Israel presented just such an opportunity.
There will be cynics who also say that with the Russian investigation possibly closing in on the Trump family and associates, this controversial move provides a perfect distraction.
I am not sure that was ever the White House thinking.
But, whatever the reasons, it is a high stakes gamble, that at best hugely complicates the peace process, or what exists of it.
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And at worse it could lead to serious violence in many parts of the region.
But Donald Trump is not averse to a gamble. It is just that this one is pretty dangerous.