There is a strong possibility that David Cameron, in one single, ill-considered, badly-timed and unnecessary speech, may have sown the seeds of his own downfall this week. And here's why.
Of all five scenarios we can imagine flowing from his speech on Britain and the EU, only one sees him surviving as party leader. So, in descending order of likelihood, let's go through them.
Scenario 1: The Conservatives lose the next election. Ed Miliband becomes prime minister; David Cameron resigns as Tory party leader.
Scenario 2: The Conservatives emerge after the next election as still the largest party in the Commons, but without an overall majority. The Lib Dems play hard ball over his commitment to an in-or-out EU referendum and demand counter-pledges that are unacceptable to the Tories. Cameron is unable to form a government, his party loses patience with him and MPs force his resignation ahead of a new election under a new leader.
Scenario 3: Either with or without an overall majority, Cameron forms a new government and tells his EU partners the UK wants to open negotiations on a new relationship. Despite Angela Merkel's apparently accommodating comments after his speech on Wednesday, when it comes to the crunch, he's told there's nothing to talk about. No negotiations, no new deal, so nothing to put to voters in a referendum. Cameron's opinion poll ratings slump, as he's accused of yet another referendum U-turn, his Euro-sceptic back-benchers rise up and force him to quit.
Scenario 4: Cameron wins the election with an overall majority in the Commons, persuades the EU to negotiate a few more opt-outs for the UK, but not enough to satisfy his back-benchers. He says he'll urge voters to back the deal anyway, but more than 100 of his MPs refuse to follow him. The party splits and he resigns.
Scenario 5: As above, but the newly-negotiated deal is so good that it satisfies even Bill Cash. All Tory MPs line up behind him to vote Yes in the referendum, and the deal is overwhelmingly approved by voters. Cameron emerges triumphant and walks across the surface of the River Thames in celebration.
So here we have a man who pretty much talked his way to the party leadership with an impressively delivered, look-no-notes speech at the Tory party conference in Blackpool in 2005 -- and who now, with a much less impressive, painfully constructed and endlessly delayed speech, may well have talked his way out of it again.
You think I'm being over-dramatic? Fine, here's the verdict from millionaire businessman and former deputy Tory chairman Michael Ashcroft, who now uses some of his wealth to pay for detailed political polling:
"Europe is not much of a priority even for those who say they might vote UKIP ... For most voters, including those who will need to vote Conservative for the first time if we are to have any hope of a majority, Europe barely registers on their list of concerns ... Tories must remember that we can only get what we want once we win an election. The more we talk about changing our relationship with Europe, the less likely it is to happen."
I suggested three weeks ago that the EU should move towards a system of concentric circles, to accommodate the very different visions of its various member states. David Cameron seems to share my analysis, although he stopped some way short of my conclusion.
He said in his speech: "We need a [EU] structure that can accommodate the diversity of its members - north, south, east, west, large, small, old and new -- some of whom are contemplating much closer economic and political integration, and many others, including Britain, who would never embrace that goal ...We must not be weighed down by an insistence on a one size fits all approach which implies that all countries want the same level of integration. The fact is that they don't and we shouldn't assert that they do."
Robin Niblett, director of the foreign policy think-tank Chatham House, makes the same point: "We did not enter the EU with the same political imperatives [as France and Germany]. We had not been invaded, we did not lose the war, and we have historical connections to all sorts of other parts of the world from our empire and commonwealth.
"To the extent that Brits are emotional about Europe, it's to be against Europe; when we're pragmatic, we're for it. Whereas you could say many continental Europeans, when they're emotional are in favor of Europe; and when they're pragmatic, they're against it. So we come at it from almost the other side of the coin."
Peter Oborne in yesterday's Daily Telegraph called Cameron's speech "a grubby piece of party management, the kind of thing Harold Wilson would have been proud of." And of course it was Labour's internal disagreements over Europe which led to Wilson's decision to call an EU in-or-out referendum in 1975, and, eventually, to the Labour split and formation of the SDP in 1981.
What was that about history repeating itself?