The tensions between Cameron and Clegg over EU
That one night of negotiation in Brussels is casting a long shadow over the coalition. It could be dubbed "the night of the long knife" as not only the coalition partners, but the European Commission, try to shift blame for an unsatisfactory outcome.
Conservative Eurosceptics applauded the prime minister in Parliament on Monday for refusing to sign a new treaty.
Polls suggest what David Cameron did - or, rather didn't do in Brussels - is popular. He is at ease with himself over his handling of the nocturnal talks.
But it was not his preferred outcome - he wanted a protocol to protect Britain's financial services industry in return for signing up to a new treaty.
So since last Friday, at the very top of the coalition, there has been an examination of what went wrong. The Conservatives and Lib Dems have been drawing very different conclusions.
Nick Clegg's non appearance in the Commons on Monday advertised the tensions in neon lights. But they are palpable behind the scenes too.
The official Lib Dem narrative goes like this:
Nick Clegg has changed the tone of his comments but has never really changed his mind. He was called from Brussels in the early hours of Friday morning only when negotiations were over. He told the prime minister he could not support the outcome. He ratcheted up the rhetoric only when Eurosceptics sounded triumphalist.
He also sympathised with David Cameron because he felt the prime minister had faced intransigence on behalf of the French and German governments and was under huge pressure from Conservative Eurosceptics not to return home empty-handed.
The unofficial narrative, from those close to Nick Clegg, is more interesting and says far more about the Cameron/Clegg relationship:
Nick Clegg had indeed signed up to the same negotiating position as the prime minister going in to the talks.
But - having spoken to key EU figures himself ahead of the summit - he had not "gameplanned" a scenario where the UK would be left in a minority of one. So he was genuinely surprised when he got the call from David Cameron telling him that was what had happened.
But the delayed reaction - from expressing disappointment, to going on television 48 hours later to denounce the outcome as "bad for Britain"' - was not simply because he was irritated by the Eurosceptics, or was under pressure from some in his party for his initially lukewarm response.
As one insider put it: "He reacted at first in the way that you would if you felt a friend had made a mistake. He then reacted as though he then had found out that the 'mistake' was that the friend had slept with his wife'."
In other words what was emerging was - in the Lib Dems' view - a sense that there had not been complete intransigence from the other EU states overnight.
This was underlined today when the President of the EU Commission said a compromise had been put forward which had been rejected.
This would have meant Britain didn't get its protocol but would get a clause in the treaty, He tabled a clause which made clear that the measures in the new fiscal compact applied only to the eurozone and wouldn't undermine the single market or allow discrimination against the financial services sector of non-Euro states.
Nick Clegg felt he had signed up to a negotiating position, not a series of inflexible demands.
But the foreign secretary William Hague -who was in Brussels during the negotiations, though not in the room with David Cameron - saw the British demands as the 'minimum' the UK would settle for.
So the anger and disappointment grew.
But senior Downing Street sources have an alternative take on events:
They say that Nick Clegg should have seen a veto coming and should not have been surprised when he got a call in the early hours of Friday in Sheffield to be told the prime minister was not signing up to treaty change.
That was because the night before David Cameron held a 45-minute meeting with President Sarkozy of France and Chancellor Merkel of Germany. The press in Brussels were briefed immediately after that meeting to be told there had been no meeting of minds and no agreement' on the British demands.
But, Downing Street maintains, Nick Clegg himself was also given the same briefing after the crucial Sarkozy/Merkel meeting and should have realised - with the French and Germans not on side - that there was a very strong possibility that Britain would have to stand alone.
Downing Street saw that meeting as the key encounter and they had made it clear to Nick Clegg that was their view.
They also insist that "our people spoke to his people" throughout the night so he could - had he chosen - known about the twists and turns in Brussels.
Nick Clegg's non-appearance at yesterday's Prime Ministerial statement had tongues wagging around Westminster.
It transpires that the PM and his deputy met for an hour beforehand and had a frank exchange of views.
But it is also clear No 10 did not share Nick Clegg's assessment that his appearance in the House of Commons would be a "distraction" - they felt that the opposite might have been the case.
So where does all this leave the relationship between David Cameron and Nick Clegg?
Well in one sense, they have been here before.
Nick Clegg was furious last Spring when he felt the prime minister had broken a promise not to campaign vigorously in the AV referendum.
A difficult moment, but the coalition survived.
And insiders say the current tensions will not undermine the coalition either.
Indeed, there is a "business-like" arrangement between the prime minister and his deputy which is still fruitful.
Those close to Nick Clegg would say he had real influence over the prime minister's statement on Europe - for example, not completely closing the door to using existing EU institutions to enforce the new fiscal pact - and delivering the address to Parliament in far from triumphalist tones.
They also point out that they had successfully watered down some potential demands before going to Brussels - such as excluding a call to repatriate some existing powers.
There is also an understanding that, increasingly, both men have to have the freedom to express themselves in ways designed to appeal to, rather than alienate, their backbenchers.
Downing Street was keen to stress that Tuesday's cabinet meeting saw Conservative and Lib Dems sharing plenty of common ground on protecting the single market and pressing the eurozone to sort out its debt problems.
And - given the Lib Dems' standing in the opinion polls in particular - there is no appetite for an early election.
But if Cameron and Clegg are the glue which hold the coalition together, their bond might just be a little less strong now.